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Subject[PATCH v2] qnx4_match: do not over run the buffer
Date
the di_fname may not terminated by '\0', use strnlen to prevent buffer
overrun

[ 513.248784] qnx4_readdir: bread failed (3718095557)
[ 513.250880] ==================================================================
[ 513.251109] BUG: KASAN: use-after-free in strlen+0x1f/0x40
[ 513.251268] Read of size 1 at addr ffff888002700000 by task find/230
[ 513.251419]
[ 513.251677] CPU: 0 PID: 230 Comm: find Not tainted 5.10.0-rc4+ #64
[ 513.251805] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-48-gd84
[ 513.252069] Call Trace:
[ 513.252310] dump_stack+0x7d/0xa3
[ 513.252443] print_address_description.constprop.0+0x1e/0x220
[ 513.252572] ? _raw_spin_lock_irqsave+0x7b/0xd0
[ 513.252681] ? _raw_write_lock_irqsave+0xd0/0xd0
[ 513.252785] ? strlen+0x1f/0x40
[ 513.252869] ? strlen+0x1f/0x40
[ 513.252955] kasan_report.cold+0x37/0x7c
[ 513.253059] ? qnx4_block_map+0x130/0x1d0
[ 513.253152] ? strlen+0x1f/0x40
[ 513.253237] strlen+0x1f/0x40
[ 513.253329] qnx4_lookup+0xab/0x220
[ 513.253431] __lookup_slow+0x103/0x220
[ 513.253531] ? vfs_unlink+0x2e0/0x2e0
[ 513.253626] ? down_read+0xd8/0x190
[ 513.253721] ? down_write_killable+0x110/0x110
[ 513.253823] ? generic_permission+0x4c/0x240
[ 513.253929] walk_component+0x214/0x2c0
[ 513.254035] ? handle_dots.part.0+0x760/0x760
[ 513.254137] ? walk_component+0x2c0/0x2c0
[ 513.254233] ? path_init+0x546/0x6b0
[ 513.254327] ? __kernel_text_address+0x9/0x30
[ 513.254430] ? unwind_get_return_address+0x2a/0x40
[ 513.254538] ? create_prof_cpu_mask+0x20/0x20
[ 513.254637] ? arch_stack_walk+0x99/0xf0
[ 513.254736] path_lookupat.isra.0+0xb0/0x240
[ 513.254840] filename_lookup+0x128/0x250
[ 513.254939] ? may_linkat+0xb0/0xb0
[ 513.255033] ? __fput+0x199/0x3c0
[ 513.255127] ? kasan_save_stack+0x32/0x40
[ 513.255224] ? kasan_save_stack+0x1b/0x40
[ 513.255323] ? kasan_unpoison_shadow+0x33/0x40
[ 513.255426] ? __kasan_kmalloc.constprop.0+0xc2/0xd0
[ 513.255538] ? getname_flags+0x100/0x2a0
[ 513.255635] vfs_statx+0xd8/0x1d0
[ 513.255728] ? vfs_getattr+0x40/0x40
[ 513.255821] ? lockref_put_return+0xb2/0x120
[ 513.255922] __do_sys_newfstatat+0x7d/0xd0
[ 513.256022] ? __ia32_sys_newlstat+0x30/0x30
[ 513.256122] ? __kasan_slab_free+0x121/0x150
[ 513.256222] ? rcu_segcblist_enqueue+0x72/0x80
[ 513.256333] ? fpregs_assert_state_consistent+0x4d/0x60
[ 513.256446] ? exit_to_user_mode_prepare+0x2d/0xf0
[ 513.256551] ? __x64_sys_newfstatat+0x39/0x60
[ 513.256651] do_syscall_64+0x33/0x40
[ 513.256750] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Co-Developed-by: Anders Larsen <al@alarsen.net>
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
---
v2: The name can grow longer than QNX4_SHORT_NAME_MAX if de is a
QNX4_FILE_LINK type and de should points to a qnx4_link_info struct, so
this is safe. We also remove redundant checks in this version.

fs/qnx4/namei.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..2bcbbd7c772e 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -40,9 +40,7 @@ static int qnx4_match(int len, const char *name,
} else {
namelen = QNX4_SHORT_NAME_MAX;
}
- thislen = strlen( de->di_fname );
- if ( thislen > namelen )
- thislen = namelen;
+ thislen = strnlen( de->di_fname, namelen );
if (len != thislen) {
return 0;
}
--
2.25.1
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