From: Andrey Ryabinin <[email protected]>
Setting smack label on file (e.g. 'attr -S -s SMACK64 -V "test" test')
triggered following spew on the kernel with KASan applied:
==================================================================
BUG: AddressSanitizer: out of bounds access in strncpy+0x28/0x60 at addr ffff8800059ad064
=============================================================================
BUG kmalloc-8 (Not tainted): kasan error
-----------------------------------------------------------------------------
Disabling lock debugging due to kernel taint
INFO: Slab 0xffffea0000166b40 objects=128 used=7 fp=0xffff8800059ad080 flags=0x4000000000000080
INFO: Object 0xffff8800059ad060 @offset=96 fp=0xffff8800059ad080
Bytes b4 ffff8800059ad050: a0 df 9a 05 00 88 ff ff 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
Object ffff8800059ad060: 74 65 73 74 6b 6b 6b a5 testkkk.
Redzone ffff8800059ad068: cc cc cc cc cc cc cc cc ........
Padding ffff8800059ad078: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
CPU: 0 PID: 528 Comm: attr Tainted: G B 3.18.0-rc1-mm1+ #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
0000000000000000 ffff8800059ad064 ffffffff81534cf2 ffff880005a5bc40
ffffffff8112fe1a 0000000100800006 0000000f059ad060 ffff880006000f90
0000000000000296 ffffea0000166b40 ffffffff8107ca97 ffff880005891060
Call Trace:
? dump_stack (lib/dump_stack.c:52)
? kasan_report_error (mm/kasan/report.c:102 mm/kasan/report.c:178)
? preempt_count_sub (kernel/sched/core.c:2651)
? __asan_load1 (mm/kasan/kasan.h:50 mm/kasan/kasan.c:248 mm/kasan/kasan.c:358)
? strncpy (lib/string.c:121)
? strncpy (lib/string.c:121)
? smk_parse_smack (security/smack/smack_access.c:457)
? setxattr (fs/xattr.c:343)
? smk_import_entry (security/smack/smack_access.c:514)
? smack_inode_setxattr (security/smack/smack_lsm.c:1093 (discriminator 1))
? security_inode_setxattr (security/security.c:602)
? vfs_setxattr (fs/xattr.c:134)
? setxattr (fs/xattr.c:343)
? setxattr (fs/xattr.c:360)
? get_parent_ip (kernel/sched/core.c:2606)
? preempt_count_sub (kernel/sched/core.c:2651)
? __percpu_counter_add (arch/x86/include/asm/preempt.h:98 lib/percpu_counter.c:90)
? get_parent_ip (kernel/sched/core.c:2606)
? preempt_count_sub (kernel/sched/core.c:2651)
? __mnt_want_write (arch/x86/include/asm/preempt.h:98 fs/namespace.c:359)
? path_setxattr (fs/xattr.c:380)
? SyS_lsetxattr (fs/xattr.c:397)
? system_call_fastpath (arch/x86/kernel/entry_64.S:423)
Read of size 1 by task attr:
Memory state around the buggy address:
ffff8800059ace80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8800059acf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8800059acf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8800059ad000: 00 fc fc fc 00 fc fc fc 05 fc fc fc 04 fc fc fc
^
ffff8800059ad080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8800059ad100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8800059ad180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
strncpy() copies one byte more than the source string has.
Fix this by passing the correct length to strncpy().
Now we can remove initialization of the last byte in 'smack' string
because kzalloc() already did this for us.
Signed-off-by: Andrey Ryabinin <[email protected]>
---
security/smack/smack_access.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 5b970ff..ad75ddf 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -452,10 +452,9 @@ char *smk_parse_smack(const char *string, int len)
return NULL;
smack = kzalloc(i + 1, GFP_KERNEL);
- if (smack != NULL) {
- strncpy(smack, string, i + 1);
- smack[i] = '\0';
- }
+ if (smack != NULL)
+ strncpy(smack, string, i);
+
return smack;
}
--
1.8.5.5
On 11/8/2014 6:48 AM, Andrey Ryabinin wrote:
> From: Andrey Ryabinin <[email protected]>
>
> Setting smack label on file (e.g. 'attr -S -s SMACK64 -V "test" test')
> triggered following spew on the kernel with KASan applied:
> ==================================================================
> BUG: AddressSanitizer: out of bounds access in strncpy+0x28/0x60 at addr ffff8800059ad064
> =============================================================================
> BUG kmalloc-8 (Not tainted): kasan error
> -----------------------------------------------------------------------------
>
> Disabling lock debugging due to kernel taint
> INFO: Slab 0xffffea0000166b40 objects=128 used=7 fp=0xffff8800059ad080 flags=0x4000000000000080
> INFO: Object 0xffff8800059ad060 @offset=96 fp=0xffff8800059ad080
>
> Bytes b4 ffff8800059ad050: a0 df 9a 05 00 88 ff ff 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
> Object ffff8800059ad060: 74 65 73 74 6b 6b 6b a5 testkkk.
> Redzone ffff8800059ad068: cc cc cc cc cc cc cc cc ........
> Padding ffff8800059ad078: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
> CPU: 0 PID: 528 Comm: attr Tainted: G B 3.18.0-rc1-mm1+ #5
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> 0000000000000000 ffff8800059ad064 ffffffff81534cf2 ffff880005a5bc40
> ffffffff8112fe1a 0000000100800006 0000000f059ad060 ffff880006000f90
> 0000000000000296 ffffea0000166b40 ffffffff8107ca97 ffff880005891060
> Call Trace:
> ? dump_stack (lib/dump_stack.c:52)
> ? kasan_report_error (mm/kasan/report.c:102 mm/kasan/report.c:178)
> ? preempt_count_sub (kernel/sched/core.c:2651)
> ? __asan_load1 (mm/kasan/kasan.h:50 mm/kasan/kasan.c:248 mm/kasan/kasan.c:358)
> ? strncpy (lib/string.c:121)
> ? strncpy (lib/string.c:121)
> ? smk_parse_smack (security/smack/smack_access.c:457)
> ? setxattr (fs/xattr.c:343)
> ? smk_import_entry (security/smack/smack_access.c:514)
> ? smack_inode_setxattr (security/smack/smack_lsm.c:1093 (discriminator 1))
> ? security_inode_setxattr (security/security.c:602)
> ? vfs_setxattr (fs/xattr.c:134)
> ? setxattr (fs/xattr.c:343)
> ? setxattr (fs/xattr.c:360)
> ? get_parent_ip (kernel/sched/core.c:2606)
> ? preempt_count_sub (kernel/sched/core.c:2651)
> ? __percpu_counter_add (arch/x86/include/asm/preempt.h:98 lib/percpu_counter.c:90)
> ? get_parent_ip (kernel/sched/core.c:2606)
> ? preempt_count_sub (kernel/sched/core.c:2651)
> ? __mnt_want_write (arch/x86/include/asm/preempt.h:98 fs/namespace.c:359)
> ? path_setxattr (fs/xattr.c:380)
> ? SyS_lsetxattr (fs/xattr.c:397)
> ? system_call_fastpath (arch/x86/kernel/entry_64.S:423)
> Read of size 1 by task attr:
> Memory state around the buggy address:
> ffff8800059ace80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8800059acf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8800059acf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff8800059ad000: 00 fc fc fc 00 fc fc fc 05 fc fc fc 04 fc fc fc
> ^
> ffff8800059ad080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8800059ad100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8800059ad180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> strncpy() copies one byte more than the source string has.
> Fix this by passing the correct length to strncpy().
>
> Now we can remove initialization of the last byte in 'smack' string
> because kzalloc() already did this for us.
>
> Signed-off-by: Andrey Ryabinin <[email protected]>
Applied to git://git.gitorious.org/smack-next/kernel.git#smack-for-3.19
> ---
> security/smack/smack_access.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> index 5b970ff..ad75ddf 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -452,10 +452,9 @@ char *smk_parse_smack(const char *string, int len)
> return NULL;
>
> smack = kzalloc(i + 1, GFP_KERNEL);
> - if (smack != NULL) {
> - strncpy(smack, string, i + 1);
> - smack[i] = '\0';
> - }
> + if (smack != NULL)
> + strncpy(smack, string, i);
> +
> return smack;
> }
>