strscpy_pad() can't be used to copy a possibly non-NUL-term string into a NUL-term string. Commit 0efc5990bca5 ("string.h: Introduce memtostr() and memtostr_pad()") provides additional information in that regard. So if this happens, the following warning is observed:
strnlen: detected buffer overflow: 65 byte read of buffer size 64 WARNING: CPU: 0 PID: 28655 at lib/string_helpers.c:1032 __fortify_report+0x96/0xc0 lib/string_helpers.c:1032 Modules linked in: CPU: 0 UID: 0 PID: 28655 Comm: syz-executor.3 Not tainted 6.12.54-syzkaller-00144-g5f0270f1ba00 #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__fortify_report+0x96/0xc0 lib/string_helpers.c:1032 Call Trace: <TASK> __fortify_panic+0x1f/0x30 lib/string_helpers.c:1039 strnlen include/linux/fortify-string.h:235 [inline] sized_strscpy include/linux/fortify-string.h:309 [inline] parse_apply_sb_mount_options fs/ext4/super.c:2504 [inline] __ext4_fill_super fs/ext4/super.c:5261 [inline] ext4_fill_super+0x3c35/0xad00 fs/ext4/super.c:5706 get_tree_bdev_flags+0x387/0x620 fs/super.c:1636 vfs_get_tree+0x93/0x380 fs/super.c:1814 do_new_mount fs/namespace.c:3553 [inline] path_mount+0x6ae/0x1f70 fs/namespace.c:3880 do_mount fs/namespace.c:3893 [inline] __do_sys_mount fs/namespace.c:4103 [inline] __se_sys_mount fs/namespace.c:4080 [inline] __x64_sys_mount+0x280/0x300 fs/namespace.c:4080 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x64/0x140 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x76/0x7e
Since s_es->s_mount_opts might be non-NUL-term, annotate it with __nonstring and use the proper memtostr_pad() routine to get its NULL-term copy.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Fixes: 8ecb790ea8c3 ("ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()") Cc: stable@vger.kernel.org Signed-off-by: Fedor Pchelkin pchelkin@ispras.ru --- fs/ext4/ext4.h | 2 +- fs/ext4/super.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 57087da6c7be..4c8698316457 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1429,7 +1429,7 @@ struct ext4_super_block { __le64 s_last_error_block; /* block involved of last error */ __u8 s_last_error_func[32] __nonstring; /* function where the error happened */ #define EXT4_S_ERR_END offsetof(struct ext4_super_block, s_mount_opts) - __u8 s_mount_opts[64]; + __u8 s_mount_opts[64] __nonstring; __le32 s_usr_quota_inum; /* inode for tracking user quota */ __le32 s_grp_quota_inum; /* inode for tracking group quota */ __le32 s_overhead_clusters; /* overhead blocks/clusters in fs */ diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 33e7c08c9529..57df129873e3 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2483,7 +2483,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb, if (!sbi->s_es->s_mount_opts[0]) return 0;
- strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts); + memtostr_pad(s_mount_opts, sbi->s_es->s_mount_opts);
fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL); if (!fc)
On Tue, 28. Oct 16:09, Fedor Pchelkin wrote:
strscpy_pad() can't be used to copy a possibly non-NUL-term string into a NUL-term string. Commit 0efc5990bca5 ("string.h: Introduce memtostr() and memtostr_pad()") provides additional information in that regard. So if this happens, the following warning is observed:
strnlen: detected buffer overflow: 65 byte read of buffer size 64 WARNING: CPU: 0 PID: 28655 at lib/string_helpers.c:1032 __fortify_report+0x96/0xc0 lib/string_helpers.c:1032 Modules linked in: CPU: 0 UID: 0 PID: 28655 Comm: syz-executor.3 Not tainted 6.12.54-syzkaller-00144-g5f0270f1ba00 #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__fortify_report+0x96/0xc0 lib/string_helpers.c:1032 Call Trace:
<TASK> __fortify_panic+0x1f/0x30 lib/string_helpers.c:1039 strnlen include/linux/fortify-string.h:235 [inline] sized_strscpy include/linux/fortify-string.h:309 [inline] parse_apply_sb_mount_options fs/ext4/super.c:2504 [inline] __ext4_fill_super fs/ext4/super.c:5261 [inline] ext4_fill_super+0x3c35/0xad00 fs/ext4/super.c:5706 get_tree_bdev_flags+0x387/0x620 fs/super.c:1636 vfs_get_tree+0x93/0x380 fs/super.c:1814 do_new_mount fs/namespace.c:3553 [inline] path_mount+0x6ae/0x1f70 fs/namespace.c:3880 do_mount fs/namespace.c:3893 [inline] __do_sys_mount fs/namespace.c:4103 [inline] __se_sys_mount fs/namespace.c:4080 [inline] __x64_sys_mount+0x280/0x300 fs/namespace.c:4080 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x64/0x140 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x76/0x7e
Since s_es->s_mount_opts might be non-NUL-term, annotate it with __nonstring and use the proper memtostr_pad() routine to get its NULL-term copy.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Fixes: 8ecb790ea8c3 ("ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()")
Though giving it a second glance I wonder what overflow problem does the commit in Fixes address?
Behavior actually stays the same: before the blamed patch in case of a non-NUL-term string kstrndup() just allocates a buffer of `size + 1` (which equals to 65 here) and no overflow is possible, as far as I can see.
If it's actually true, maybe we'd better just revert 8ecb790ea8c3 ("ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()") ?
Cc: stable@vger.kernel.org Signed-off-by: Fedor Pchelkin pchelkin@ispras.ru
fs/ext4/ext4.h | 2 +- fs/ext4/super.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 57087da6c7be..4c8698316457 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1429,7 +1429,7 @@ struct ext4_super_block { __le64 s_last_error_block; /* block involved of last error */ __u8 s_last_error_func[32] __nonstring; /* function where the error happened */ #define EXT4_S_ERR_END offsetof(struct ext4_super_block, s_mount_opts)
- __u8 s_mount_opts[64];
- __u8 s_mount_opts[64] __nonstring; __le32 s_usr_quota_inum; /* inode for tracking user quota */ __le32 s_grp_quota_inum; /* inode for tracking group quota */ __le32 s_overhead_clusters; /* overhead blocks/clusters in fs */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 33e7c08c9529..57df129873e3 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2483,7 +2483,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb, if (!sbi->s_es->s_mount_opts[0]) return 0;
- strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
- memtostr_pad(s_mount_opts, sbi->s_es->s_mount_opts);
fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL); if (!fc) -- 2.51.0
linux-stable-mirror@lists.linaro.org
-
Fedor Pchelkin