malloc: free list modified: proc (2)

Status: upstream: reported on 2026/09/04 11:38
Reported-by: syzbot+5ddc8419435e0130592c@syzkaller.appspotmail.com
First crash: 15d, last: 15d
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
openbsd malloc: free list modified: proc -1 1 708d 708d 0/4 auto-obsoleted due to no activity on 2025/01/10 01:44

Sample crash report:
panic: Data modified on freelist: word 6 of object 0xffff8000015e5540 size 0x30 previous type proc (0x0 != 0xdeafbead)

Stopped at      db_enter+0x25:  addq    $0x8,%rsp
    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
*199065  52289      0         0x2          0    0  syz-executor
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:438
panic(ffffffff83454f5f) at panic+0x1cf sys/kern/subr_prf.c:198
malloc(30,7f,9) at malloc+0xdb6 sys/kern/kern_malloc.c:357
dopselect(ffff80002a7607d8,35,78fdbc67d1e0,0,0,ffff80002a7bf600,7ac71704e2df14e4,ffff80002a7bf690) at dopselect+0xe4 sys/kern/sys_generic.c:619
sys_pselect(ffff80002a7607d8,ffff80002a7bf740,ffff80002a7bf690) at sys_pselect+0x25a sys/kern/sys_generic.c:593
syscall(ffff80002a7bf740) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff80002a7bf740) at syscall+0x962 sys/arch/amd64/amd64/trap.c:791
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0x78fdbc67d190, count: 8
https://www.openbsd.org/ddb.html describes the minimum info required in bug
reports.  Insufficient info makes it difficult to find and fix bugs.
ddb> 
ddb> set $lines = 0
ddb> set $maxwidth = 0
ddb> show panic
*cpu0: Data modified on freelist: word 6 of object 0xffff8000015e5540 size 0x30 previous type proc (0x0 != 0xdeafbead)

ddb> show kasan
No such command
ddb> trace
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:438
panic(ffffffff83454f5f) at panic+0x1cf sys/kern/subr_prf.c:198
malloc(30,7f,9) at malloc+0xdb6 sys/kern/kern_malloc.c:357
dopselect(ffff80002a7607d8,35,78fdbc67d1e0,0,0,ffff80002a7bf600,7ac71704e2df14e4,ffff80002a7bf690) at dopselect+0xe4 sys/kern/sys_generic.c:619
sys_pselect(ffff80002a7607d8,ffff80002a7bf740,ffff80002a7bf690) at sys_pselect+0x25a sys/kern/sys_generic.c:593
syscall(ffff80002a7bf740) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff80002a7bf740) at syscall+0x962 sys/arch/amd64/amd64/trap.c:791
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0x78fdbc67d190, count: -7
ddb> show registers
rdi                                0
rsi                              0x1
rbp               0xffff80002a7bf130
rbx               0xffff8000015e5540
rdx                                0
rcx                                0
rax               0xffff80002a7607d8
r8                 0x101010101010101
r9                0x8080808080808080
r10               0xc9126d04d997788e
r11               0xda94a97233f284e3
r12                                0
r13               0xffffffff83af2b40    kmemstats+0x1fc0
r14                                0
r15                              0x1
rip               0xffffffff8252c7b5    db_enter+0x25
cs                               0x8
rflags                         0x246
rsp               0xffff80002a7bf120
ss                              0x10
db_enter+0x25:  addq    $0x8,%rsp
ddb> show proc
PROC (syz-executor) tid=199065 pid=52289 tcnt=1 stat=onproc
    flags process=2<EXEC> proc=0
    runpri=24, usrpri=50, slppri=24, nice=20
    wchan=0x0, wmesg=, ps_single=0x0 scnt=0 ecnt=0
    forw=0xffffffffffffffff, list=0xffff80002a761a00,0xffff80002a760550
    process=0xffff80002a77d210 user=0xffff80002a7ba000, vmspace=0xffffee007f226000
    estcpu=36, cpticks=6, pctcpu=0.0, user=0, sys=5, intr=1
ddb> ps
   PID     TID   PPID   UID  S      PRLAGS     PFLAGS WAIT      COMMAND
 54877  137062  53442     0  2           0          0           syz-executor
 14921   72807   4812     0  3           0          0 kernel: protection fault trap, code=0
Faulted in DDB; continuing...
ddb> show all locks
No such command
ddb> show malloc
           Type InUse  MemUse  HighUse   Limit  Requests Type Lim
         devbuf 11037  12106K   12349K 166960K     12468        0
            pcb    18     12K      12K 166960K        57        0
         rtable   237      6K       8K 166960K       558        0
             pf    31     13K      20K 166960K        92        0
         ifaddr    43      7K       8K 166960K        72        0
        ifgroup    47      1K       2K 166960K        86        0
         sysctl     1      1K       9K 166960K         5        0
       counters    33     17K      17K 166960K        43        0
       ioctlops     0      0K       4K 166960K       127        0
            iov     0      0K      14K 166960K        18        0
          mount     1      1K       1K 166960K         1        0
            log     0      0K       0K 166960K         4        0
         vnodes  1302     82K      82K 166960K      1678        0
      UFS quota     1     32K      32K 166960K         1        0
      UFS mount     5     36K      36K 166960K         5        0
            shm     2      1K       5K 166960K         6        0
         VM map     2      1K       1K 166960K         2        0
            sem    27      1K       1K 166960K        35        0
        dirhash    12      2K       2K 166960K        18        0
           ACPI  1692    195K     286K 166960K     12470        0
      file desc    17     61K     106K 166960K       487        0
          sigio     0      0K       0K 166960K         3        0
           proc    60     59K     124K 166960K       648        0
        subproc    72      4K       4K 166960K       117        0
    NFS srvsock     1      0K       0K 166960K         1        0
     NFS daemon     1     16K      16K 166960K         1        0
    ip_moptions     0      0K       0K 166960K        30        0
       in_multi   103      6K       6K 166960K       162        0
    ether_multi     1      0K       0K 166960K         3        0
            mrt     0      0K       0K 166960K         9        0
    ISOFS mount     1     32K      32K 166960K         1        0
  MSDOSFS mount     1     16K      16K 166960K         1        0
           ttys    73    334K     334K 166960K        73        0
           exec     0      0K       1K 166960K       442        0
   fusefs mount     1     32K      32K 166960K         1        0
     pfkey data     0      0K       0K 166960K         1        0
            tdb     3      0K       0K 166960K         3        0
        VM swap     8     62K      64K 166960K        10        0
       UVM amap   236    160K     164K 166960K      5565        0
       UVM aobj    11      2K       2K 166960K        12        0
     pinsyscall    38     76K      98K 166960K      1713        0
        memdesc     1      4K       4K 166960K         1        0
    crypto data     1      1K       1K 166960K         1        0
    ip6_options     0      0K       0K 166960K        25        0
            NDP    13      0K       2K 166960K        47        0
           temp    36   9106K    9170K 166960K      5686        0
         kqueue    15     24K      26K 166960K        58        0
      SYN cache     2     16K      16K 166960K         2        0
ddb> show all pools
Name      Size Requests Fail Releases Pgreq Pgrel Npage Hiwat Minpg Maxpg Idle
rtpcb      120       61    0       57     1     0     1     1     0     8    0
rtentry    136      183    0       74     4     0     4     4     0     8    0
unpcb      144      132    0      108     1     0     1     1     0     8    0
syncache   336        8    0        8     1     0     1     1     0     8    1
tcpcb      736       96    0       88     1     0     1     1     0     8    0
arp         96       35    0       17     1     0     1     1     0     8    0
ipq         40        1    0        0     1     0     1     1     0     8    0
ipqe        40        1    0        0     1     0     1     1     0     8    0
inpcb      328      264    0      251     2     0     2     2     0     8    0
nd6        112       42    0       16     1     0     1     1     0     8    0
pkpcb       40       35    0       35     1     0     1     1     0     8    1
kcovpl      48       13    0        5     1     0     1     1     0     8    0
ppxss      1072       3    0        3     1     0     1     1     0     8    1
pfstscr     40        2    0        2     1     0     1     1     0     8    1
pffrag     232        1    0        0     1     0     1     1     0   482    0
pffrnode    88        1    0        0     1     0     1     1     0     8    0
pffrent     40        1    0        0     1     0     1     1     0     8    0
pfrktable  1344       3    0        3     1     0     1     1     0     8    1
pfanchor   1288       7    0        2     1     0     1     1     0     8    0
pftag       88        1    0        0     1     0     1     1     0     8    0
pfqueue    320        1    0        1     1     0     1     1     0     8    1
pfstkey    128        2    0        2     1     0     1     1     0     8    1
pfstate    384        1    0        1     1     0     1     1     0     8    1
pfrule     1360       4    0        4     1     0     1     1     0     8    1
art_heap8  4096       1    0        0     1     0     1     1     0     8    0
art_heap4  256      691    0      235    32     0    32    32     0     8    3
art_table   40      692    0      235     6     0     6     6     0     8    0
art_node    32      183    0       87     1     0     1     1     0     8    0
sysvmsgpl   40        1    0        1     1     0     1     1     0     8    1
semupl     112        7    0        7     1     0     1     1     0     8    1
semapl      72       32    0        7     1     0     1     1     0     8    0
shmpl      112        9    0        1     1     0     1     1     0     8    0
dirhash    1024      21    0        4     3     0     3     3     0     8    0
dino2pl    256     2079    0      609    93     0    93    93     0     8    1
ffsino     256     2079    0      609    93     0    93    93     0     8    1
nchpl      144     2608    0      887    64     0    64    64     0     8    0
vnodes     216     2362    0        0   132     0   132   132     0     8    0
namei      1024    8982    0     8982     4     0     4     4     0     8    4
pfiaddrpl  120        1    0        1     1     0     1     1     0     8    1
kstatmem   264       43    0       20     2     0     2     2     0     8    0
scsiplug    72        2    0        2     1     0     1     1     0     8    1
scxspl     216     9840    0     9839     4     0     4     4     1     8    3
plimitpl   152       53    0       37     1     0     1     1     0     8    0
sigapl     424      762    0      719     6     0     6     6     0     8    0
knotepl    120    12347    0    12043    10     0    10    10     0     8    0
kqueuepl   184       90    0       79     1     0     1     1     0     8    0
pipepl     304      153    0      126     3     0     3     3     0     8    0
fdescpl    448      748    0      719     5     0     5     5     0     8    1
filepl     120     2970    0     2737     8     0     8     8     0     8    0
lockfpl    104      131    0      127     1     0     1     1     0     8    0
lockfspl    48       62    0       59     1     0     1     1     0     8    0
sessionpl  144       47    0       36     1     0     1     1     0     8    0
pgrppl      48       63    0       44     1     0     1     1     0     8    0
ucredpl    104      306    0      295     1     0     1     1     0     8    0
zombiepl   144      720    0      719     1     0     1     1     0     8    0
processpl  1152     762    0      719     4     0     4     4     0     8    0
procpl     664     1123    0     1066     6     0     6     6     0     8    0
sosppl     176        4    0        4     1     0     1     1     0     8    1
sockpl     552      499    0      456     5     0     5     5     0     8    1
mcl64k     65536     70    0       69     1     0     1     1     0     8    0
mcl16k     16384     46    0       44     1     0     1     1     0     8    0
mcl12k     12288     11    0       11     1     0     1     1     0     8    1
mcl9k128   9344       2    0        2     1     0     1     1     0     8    1
mcl8k      8192      33    0       33     1     0     1     1     0     8    1
mcl4k      4096    2976    0     2926    13     0    13    13     0     8    6
mcl2k2     2112       1    0        1     1     0     1     1     0     8    1
mcl2k      2048     407    0      405     1     0     1     1     0     8    0
mextrefs    64      306    0      304     1     0     1     1     0     8    0
mtagpl      96        6    0        6     1     0     1     1     0     8    1
mbufpl     256     7684    0     7522    12     0    12    12     0     8    0
bufpl      272     3161    0      107   204     0   204   204     0     8    0
anonpl      24   122789    0   116524    47     0    47    47     0   187    3
amapchunkpl 152   17121    0    16522    27     0    27    27     0   158    1
amappl16   200     2328    0     2143    15     1    14    14     0     8    0
amappl15   192        5    0        5     1     0     1     1     0     8    1
amappl14   184      513    0      512     1     0     1     1     0     8    0
amappl13   176      137    0      127     1     0     1     1     0     8    0
amappl12   168     1004    0      977     2     0     2     2     0     8    0
amappl11   160        4    0        4     1     0     1     1     0     8    1
amappl10   152       57    0       46     1     0     1     1     0     8    0
amappl9    144      272    0      272     1     0     1     1     0     8    1
amappl8    136      114    0      113     1     0     1     1     0     8    0
amappl7    128      155    0      144     1     0     1     1     0     8    0
amappl6    120      199    0      198     1     0     1     1     0     8    0
amappl5    112      105    0       98     1     0     1     1     0     8    0
amappl4    104      280    0      261     1     0     1     1     0     8    0
amappl3     96     3024    0     2929     3     0     3     3     0     8    0
amappl2     88      848    0      779     2     0     2     2     0     8    0
amappl1     80    11832    0    11286    13     0    13    13     0     8    1
amappl      88     4753    0     4580     5     0     5     5     0    92    0
uvmvnodes   80      110    0        0     3     0     3     3     0     8    0
dma4096    4096       1    0        1     1     0     1     1     0     8    1
dma1024    1024       1    0        0     1     0     1     1     0     8    0
dma256     256        6    0        6     1     0     1     1     0     8    1
dma128     128      253    0      253     1     0     1     1     0     8    1
dma64       64        6    0        6     1     0     1     1     0     8    1
dma32       32        7    0        7     1     0     1     1     0     8    1
dma16       16       18    0       17     1     0     1     1     0     8    0
aobjpl      72       11    0        1     1     0     1     1     0     8    0
uaddrrnd    24      748    0      719     1     0     1     1     0     8    0
uaddrbest   32        2    0        0     1     0     1     1     0     8    0
uaddr       24      748    0      719     1     0     1     1     0     8    0
vmmpekpl   168     7382    0     7337     3     0     3     3     0     8    0
vmmpepl    168    57601    0    55646    91     0    91    91     0   357    2
vmsppl     368      747    0      719     4     0     4     4     0     8    1
rwobjpl     40    18364    0    17229    13     0    13    13     0     8    0
pdppl      4096    1502    0     1438   100    32    68    82     0     8    4
pvpl        32   354683    0   340403   131     0   131   131     0   265   12
pmappl     216      747    0      719     3     0     3     3     0     8    0
extentpl    40       45    0       27     1     0     1     1     0     8    0
phpool     112      574    0       32    16     0    16    16     0     8    0
ddb> machine ddbcpu 0
No such command
ddb> trace
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:438
panic(ffffffff83454f5f) at panic+0x1cf sys/kern/subr_prf.c:198
malloc(30,7f,9) at malloc+0xdb6 sys/kern/kern_malloc.c:357
dopselect(ffff80002a7607d8,35,78fdbc67d1e0,0,0,ffff80002a7bf600,7ac71704e2df14e4,ffff80002a7bf690) at dopselect+0xe4 sys/kern/sys_generic.c:619
sys_pselect(ffff80002a7607d8,ffff80002a7bf740,ffff80002a7bf690) at sys_pselect+0x25a sys/kern/sys_generic.c:593
syscall(ffff80002a7bf740) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff80002a7bf740) at syscall+0x962 sys/arch/amd64/amd64/trap.c:791
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0x78fdbc67d190, count: -7
ddb> machine ddbcpu 1
No such command
ddb> trace
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:438
panic(ffffffff83454f5f) at panic+0x1cf sys/kern/subr_prf.c:198
malloc(30,7f,9) at malloc+0xdb6 sys/kern/kern_malloc.c:357
dopselect(ffff80002a7607d8,35,78fdbc67d1e0,0,0,ffff80002a7bf600,7ac71704e2df14e4,ffff80002a7bf690) at dopselect+0xe4 sys/kern/sys_generic.c:619
sys_pselect(ffff80002a7607d8,ffff80002a7bf740,ffff80002a7bf690) at sys_pselect+0x25a sys/kern/sys_generic.c:593
syscall(ffff80002a7bf740) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff80002a7bf740) at syscall+0x962 sys/arch/amd64/amd64/trap.c:791
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0x78fdbc67d190, count: -7

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/04 11:38 openbsd f872d3b32498 44dda43b .config console log report [disk image] [bsd.gdb] [kernel image] ci-openbsd-main malloc: free list modified: proc
* Struck through repros no longer work on HEAD.