Re: [PATCH] apparmor: Fix string overrun due to missing termination

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Mar 19, 2026 at 02:24:32PM +0800, Daniel J Blueman wrote:
> When booting Ubuntu 26.04 with Linux 7.0-rc4 on an ARM64 Qualcomm
> Snapdragon X1 we see a string buffer overrun:
> 
> BUG: KASAN: slab-out-of-bounds in aa_dfa_match (security/apparmor/match.c:535)
> Read of size 1 at addr ffff0008901cc000 by task snap-update-ns/2120
> 
> CPU: 5 UID: 60578 PID: 2120 Comm: snap-update-ns Not tainted 7.0.0-rc4+ #22 PREEMPTLAZY
> Hardware name: LENOVO 83ED/LNVNB161216, BIOS NHCN60WW 09/11/2025
> Call trace:
> show_stack (arch/arm64/kernel/stacktrace.c:501) (C)
> dump_stack_lvl (lib/dump_stack.c:122)
> print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
> kasan_report (mm/kasan/report.c:597)
> __asan_report_load1_noabort (mm/kasan/report_generic.c:378)
> aa_dfa_match (security/apparmor/match.c:535)
> match_mnt_path_str (security/apparmor/mount.c:244 security/apparmor/mount.c:336)
> match_mnt (security/apparmor/mount.c:371)
> aa_bind_mount (security/apparmor/mount.c:447 (discriminator 4))
> apparmor_sb_mount (security/apparmor/lsm.c:719 (discriminator 1))
> security_sb_mount (security/security.c:1062 (discriminator 31))
> path_mount (fs/namespace.c:4101)
> __arm64_sys_mount (fs/namespace.c:4172 fs/namespace.c:4361 fs/namespace.c:4338 fs/namespace.c:4338)
> invoke_syscall.constprop.0 (arch/arm64/kernel/syscall.c:35 arch/arm64/kernel/syscall.c:49)
> el0_svc_common.constprop.0 (./include/linux/thread_info.h:142 (discriminator 2) arch/arm64/kernel/syscall.c:140 (discriminator 2))
> do_el0_svc (arch/arm64/kernel/syscall.c:152)
> el0_svc (arch/arm64/kernel/entry-common.c:80 arch/arm64/kernel/entry-common.c:725)
> el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:744)
> el0t_64_sync (arch/arm64/kernel/entry.S:596)
> 
> Allocated by task 2120:
> kasan_save_stack (mm/kasan/common.c:58)
> kasan_save_track (./arch/arm64/include/asm/current.h:19 mm/kasan/common.c:70 mm/kasan/common.c:79)
> kasan_save_alloc_info (mm/kasan/generic.c:571)
> __kasan_kmalloc (mm/kasan/common.c:419)
> __kmalloc_noprof (./include/linux/kasan.h:263 mm/slub.c:5260 mm/slub.c:5272)
> aa_get_buffer (security/apparmor/lsm.c:2201)
> aa_bind_mount (security/apparmor/mount.c:442)
> apparmor_sb_mount (security/apparmor/lsm.c:719 (discriminator 1))
> security_sb_mount (security/security.c:1062 (discriminator 31))
> path_mount (fs/namespace.c:4101)
> __arm64_sys_mount (fs/namespace.c:4172 fs/namespace.c:4361 fs/namespace.c:4338 fs/namespace.c:4338)
> invoke_syscall.constprop.0 (arch/arm64/kernel/syscall.c:35 arch/arm64/kernel/syscall.c:49)
> el0_svc_common.constprop.0 (./include/linux/thread_info.h:142 (discriminator 2) arch/arm64/kernel/syscall.c:140 (discriminator 2))
> do_el0_svc (arch/arm64/kernel/syscall.c:152)
> el0_svc (arch/arm64/kernel/entry-common.c:80 arch/arm64/kernel/entry-common.c:725)
> el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:744)
> el0t_64_sync (arch/arm64/kernel/entry.S:596)
> 
> The buggy address belongs to the object at ffff0008901ca000
> which belongs to the cache kmalloc-rnd-06-8k of size 8192
> The buggy address is located 0 bytes to the right of
> allocated 8192-byte region [ffff0008901ca000, ffff0008901cc000)
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9101c8
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:-1 pincount:0
> flags: 0x8000000000000040(head|zone=2)
> page_type: f5(slab)
> raw: 8000000000000040 ffff000800016c40 fffffdffe2d14e10 ffff000800015c70
> raw: 0000000000000000 0000000800010001 00000000f5000000 0000000000000000
> head: 8000000000000040 ffff000800016c40 fffffdffe2d14e10 ffff000800015c70
> head: 0000000000000000 0000000800010001 00000000f5000000 0000000000000000
> head: 8000000000000003 fffffdffe2407201 fffffdffffffffff 00000000ffffffff
> head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
> ffff0008901cbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff0008901cbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff0008901cc000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ^
> ffff0008901cc080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff0008901cc100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> 
> This was introduced by previous incorrect conversion from strcpy(). Fix it
> by adding the missing terminator.
> 
> Signed-off-by: Daniel J Blueman <daniel@quora.org>
> Fixes: 93d4dbdc8da0 ("apparmor: Replace deprecated strcpy in d_namespace_path")
> ---
>  security/apparmor/path.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/security/apparmor/path.c b/security/apparmor/path.c
> index 65a0ca5cc1bd..2494e8101538 100644
> --- a/security/apparmor/path.c
> +++ b/security/apparmor/path.c
> @@ -164,14 +164,16 @@ static int d_namespace_path(const struct path *path, char *buf, char **name,
>  	}
>  
>  out:
> -	/* Append "/" to directory paths, except for root "/" which
> -	 * already ends in a slash.
> +	/* Append "/" to directory paths and reterminate string, except for
> +	 * root "/" which already ends in a slash.
>  	 */
>  	if (!error && isdir) {
>  		bool is_root = (*name)[0] == '/' && (*name)[1] == '\0';
>  
> -		if (!is_root)
> +		if (!is_root) {
>  			buf[aa_g_path_max - 2] = '/';
> +			buf[aa_g_path_max - 1] = '\0';
> +		}
>  	}
>  
>  	return error;
> -- 
> 2.53.0
> 
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>