https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263934
Bug ID: 263934
Summary: buffer overflow in ffs_sbget() if superblock fields
are broken
Product: Base System
Version: Unspecified
Hardware: Any
OS: Any
Status: New
Severity: Affects Some People
Priority: ---
Component: kern
Assignee: [email protected]
Reporter: [email protected]
Created attachment 233866
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=233866&action=edit
a disk image that causes a buffer overflow during tasting, due to unexpected
FFS superblock content
ffs_sbget() allocates fs->fs_cssize bytes to hold fs_csp:
size = fs->fs_cssize;
...
if ((space = UFS_MALLOC(size, filltype, M_WAITOK)) == NULL) {
but it can copy a whole fragment into that space:
for (i = 0; i < blks; i += fs->fs_frag) {
...;
size = (blks - i) * fs->fs_fsize;
...;
error = (*readfunc)(devfd,
dbtob(fsbtodb(fs, fs->fs_csaddr + i)), (void **)&buf,
size);
...;
memcpy(space, buf, size);
If fs_cssize is smaller than fs_fsize, the memcpy() can write
attacker-supplied bytes beyond the end of space.
I've attached a disk image containing garbage that looks enough like
FFS for taste to proceed, with fs_cssize = 16 and fs_fsize = 5120.
# uname -a
FreeBSD 14.0-CURRENT FreeBSD 14.0-CURRENT #224
main-n250919-29f81bc20825-dirty: Thu May 12 04:42:56 EDT 2022
rtm@zika:/usr/obj/usr/rtm/symbsd/src/riscv.riscv64/sys/RTM riscv
# mdconfig -f taste6b.img
Memory modified after free 0xffffffd000852b40(24) val=ffffffff @
0xffffffd000852b40
panic: Fatal page fault at 0xffffffc00051b2b0: 0xffffffff00000070
cpuid = 0
time = 1651916658
KDB: stack backtrace:
db_trace_self() at db_trace_self
db_trace_self_wrapper() at db_trace_self_wrapper+0x38
kdb_backtrace() at kdb_backtrace+0x2c
vpanic() at vpanic+0x16e
panic() at panic+0x2a
page_fault_handler() at page_fault_handler+0x1aa
do_trap_supervisor() at do_trap_supervisor+0x76
cpu_exception_handler_supervisor() at cpu_exception_handler_supervisor+0x70
--- exception 13, tval = 0xffffffff00000070
mtrash_ctor() at mtrash_ctor+0x86
item_ctor() at item_ctor+0xa0
cache_alloc_item() at cache_alloc_item+0x5a
uma_zalloc_arg() at uma_zalloc_arg+0x58
uma_zalloc() at uma_zalloc+0x10
malloc() at malloc+0x80
ffs_sbget() at ffs_sbget+0x1e8
g_label_ufs_taste_common() at g_label_ufs_taste_common+0x6c
g_label_ufs_volume_taste() at g_label_ufs_volume_taste+0xe
g_label_taste() at g_label_taste+0x198
g_new_provider_event() at g_new_provider_event+0xb8
one_event() at one_event+0x106
g_run_events() at g_run_events+0x8a
g_event_procbody() at g_event_procbody+0x56
fork_exit() at fork_exit+0x80
fork_trampoline() at fork_trampoline+0xa
KDB: enter: panic
[ thread pid 13 tid 100017 ]
Stopped at breakpoint+0xa: c.ldsp s0,0(sp)
db>
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