2022-08-22 10:06:30

by Luís Henriques

[permalink] [raw]
Subject: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0

When walking through an inode extents, the ext4_ext_binsearch_idx() function
assumes that the extent header has been previously validated. However, there
are no checks that verify that the number of entries (eh->eh_entries) is
non-zero when depth is > 0. And this will lead to problems because the
EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this:

[ 135.245946] ------------[ cut here ]------------
[ 135.247579] kernel BUG at fs/ext4/extents.c:2258!
[ 135.249045] invalid opcode: 0000 [#1] PREEMPT SMP
[ 135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4
[ 135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
[ 135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0
[ 135.256475] Code:
[ 135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246
[ 135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023
[ 135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c
[ 135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c
[ 135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024
[ 135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000
[ 135.272394] FS: 00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
[ 135.274510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0
[ 135.277952] Call Trace:
[ 135.278635] <TASK>
[ 135.279247] ? preempt_count_add+0x6d/0xa0
[ 135.280358] ? percpu_counter_add_batch+0x55/0xb0
[ 135.281612] ? _raw_read_unlock+0x18/0x30
[ 135.282704] ext4_map_blocks+0x294/0x5a0
[ 135.283745] ? xa_load+0x6f/0xa0
[ 135.284562] ext4_mpage_readpages+0x3d6/0x770
[ 135.285646] read_pages+0x67/0x1d0
[ 135.286492] ? folio_add_lru+0x51/0x80
[ 135.287441] page_cache_ra_unbounded+0x124/0x170
[ 135.288510] filemap_get_pages+0x23d/0x5a0
[ 135.289457] ? path_openat+0xa72/0xdd0
[ 135.290332] filemap_read+0xbf/0x300
[ 135.291158] ? _raw_spin_lock_irqsave+0x17/0x40
[ 135.292192] new_sync_read+0x103/0x170
[ 135.293014] vfs_read+0x15d/0x180
[ 135.293745] ksys_read+0xa1/0xe0
[ 135.294461] do_syscall_64+0x3c/0x80
[ 135.295284] entry_SYSCALL_64_after_hwframe+0x46/0xb0

This patch simply adds an extra check in __ext4_ext_check(), verifying that
eh_entries is not 0 when eh_depth is > 0.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215941
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216283
Cc: Baokun Li <[email protected]>
Signed-off-by: Luís Henriques <[email protected]>
---
fs/ext4/extents.c | 4 ++++
1 file changed, 4 insertions(+)

Changes since v3:
- Fixed typo (I had 'eh_depth' instead of 'depth')

Changes since v2:
- Dropped usage of le16_to_cpu() because we're comparing values against 0
- Use 'depth' instead of 'eh->eh_depth' because we've checked earlier that
both have the same value.


diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c148bb97b527..5235974126bd 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -460,6 +460,10 @@ static int __ext4_ext_check(const char *function, unsigned int line,
error_msg = "invalid eh_entries";
goto corrupted;
}
+ if (unlikely((eh->eh_entries == 0) && (depth > 0))) {
+ error_msg = "eh_entries is 0 but eh_depth is > 0";
+ goto corrupted;
+ }
if (!ext4_valid_extent_entries(inode, eh, lblk, &pblk, depth)) {
error_msg = "invalid extent entries";
goto corrupted;


2022-09-12 14:42:19

by Luís Henriques

[permalink] [raw]
Subject: Re: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0


Ping?

I have written an fstest for this fix, but since it generates a corrupted
image that crashes the kernel I'd rather have the bug fixed before
submitting it.

Cheers,
--
Luís

Luís Henriques <[email protected]> writes:

> When walking through an inode extents, the ext4_ext_binsearch_idx() function
> assumes that the extent header has been previously validated. However, there
> are no checks that verify that the number of entries (eh->eh_entries) is
> non-zero when depth is > 0. And this will lead to problems because the
> EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this:
>
> [ 135.245946] ------------[ cut here ]------------
> [ 135.247579] kernel BUG at fs/ext4/extents.c:2258!
> [ 135.249045] invalid opcode: 0000 [#1] PREEMPT SMP
> [ 135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4
> [ 135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
> [ 135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0
> [ 135.256475] Code:
> [ 135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246
> [ 135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023
> [ 135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c
> [ 135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c
> [ 135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024
> [ 135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000
> [ 135.272394] FS: 00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
> [ 135.274510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0
> [ 135.277952] Call Trace:
> [ 135.278635] <TASK>
> [ 135.279247] ? preempt_count_add+0x6d/0xa0
> [ 135.280358] ? percpu_counter_add_batch+0x55/0xb0
> [ 135.281612] ? _raw_read_unlock+0x18/0x30
> [ 135.282704] ext4_map_blocks+0x294/0x5a0
> [ 135.283745] ? xa_load+0x6f/0xa0
> [ 135.284562] ext4_mpage_readpages+0x3d6/0x770
> [ 135.285646] read_pages+0x67/0x1d0
> [ 135.286492] ? folio_add_lru+0x51/0x80
> [ 135.287441] page_cache_ra_unbounded+0x124/0x170
> [ 135.288510] filemap_get_pages+0x23d/0x5a0
> [ 135.289457] ? path_openat+0xa72/0xdd0
> [ 135.290332] filemap_read+0xbf/0x300
> [ 135.291158] ? _raw_spin_lock_irqsave+0x17/0x40
> [ 135.292192] new_sync_read+0x103/0x170
> [ 135.293014] vfs_read+0x15d/0x180
> [ 135.293745] ksys_read+0xa1/0xe0
> [ 135.294461] do_syscall_64+0x3c/0x80
> [ 135.295284] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> This patch simply adds an extra check in __ext4_ext_check(), verifying that
> eh_entries is not 0 when eh_depth is > 0.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215941
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216283
> Cc: Baokun Li <[email protected]>
> Signed-off-by: Luís Henriques <[email protected]>
> ---
> fs/ext4/extents.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> Changes since v3:
> - Fixed typo (I had 'eh_depth' instead of 'depth')
>
> Changes since v2:
> - Dropped usage of le16_to_cpu() because we're comparing values against 0
> - Use 'depth' instead of 'eh->eh_depth' because we've checked earlier that
> both have the same value.
>
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index c148bb97b527..5235974126bd 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -460,6 +460,10 @@ static int __ext4_ext_check(const char *function, unsigned int line,
> error_msg = "invalid eh_entries";
> goto corrupted;
> }
> + if (unlikely((eh->eh_entries == 0) && (depth > 0))) {
> + error_msg = "eh_entries is 0 but eh_depth is > 0";
> + goto corrupted;
> + }
> if (!ext4_valid_extent_entries(inode, eh, lblk, &pblk, depth)) {
> error_msg = "invalid extent entries";
> goto corrupted;

2022-09-19 15:14:31

by Jan Kara

[permalink] [raw]
Subject: Re: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0

On Mon 22-08-22 10:42:35, Lu?s Henriques wrote:
> When walking through an inode extents, the ext4_ext_binsearch_idx() function
> assumes that the extent header has been previously validated. However, there
> are no checks that verify that the number of entries (eh->eh_entries) is
> non-zero when depth is > 0. And this will lead to problems because the
> EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this:
>
> [ 135.245946] ------------[ cut here ]------------
> [ 135.247579] kernel BUG at fs/ext4/extents.c:2258!
> [ 135.249045] invalid opcode: 0000 [#1] PREEMPT SMP
> [ 135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4
> [ 135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
> [ 135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0
> [ 135.256475] Code:
> [ 135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246
> [ 135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023
> [ 135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c
> [ 135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c
> [ 135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024
> [ 135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000
> [ 135.272394] FS: 00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
> [ 135.274510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0
> [ 135.277952] Call Trace:
> [ 135.278635] <TASK>
> [ 135.279247] ? preempt_count_add+0x6d/0xa0
> [ 135.280358] ? percpu_counter_add_batch+0x55/0xb0
> [ 135.281612] ? _raw_read_unlock+0x18/0x30
> [ 135.282704] ext4_map_blocks+0x294/0x5a0
> [ 135.283745] ? xa_load+0x6f/0xa0
> [ 135.284562] ext4_mpage_readpages+0x3d6/0x770
> [ 135.285646] read_pages+0x67/0x1d0
> [ 135.286492] ? folio_add_lru+0x51/0x80
> [ 135.287441] page_cache_ra_unbounded+0x124/0x170
> [ 135.288510] filemap_get_pages+0x23d/0x5a0
> [ 135.289457] ? path_openat+0xa72/0xdd0
> [ 135.290332] filemap_read+0xbf/0x300
> [ 135.291158] ? _raw_spin_lock_irqsave+0x17/0x40
> [ 135.292192] new_sync_read+0x103/0x170
> [ 135.293014] vfs_read+0x15d/0x180
> [ 135.293745] ksys_read+0xa1/0xe0
> [ 135.294461] do_syscall_64+0x3c/0x80
> [ 135.295284] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> This patch simply adds an extra check in __ext4_ext_check(), verifying that
> eh_entries is not 0 when eh_depth is > 0.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215941
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216283
> Cc: Baokun Li <[email protected]>
> Signed-off-by: Lu?s Henriques <[email protected]>

The patch looks good to me. Thanks for the fix. Feel free to add:

Reviewed-by: Jan Kara <[email protected]>

Honza

> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index c148bb97b527..5235974126bd 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -460,6 +460,10 @@ static int __ext4_ext_check(const char *function, unsigned int line,
> error_msg = "invalid eh_entries";
> goto corrupted;
> }
> + if (unlikely((eh->eh_entries == 0) && (depth > 0))) {
> + error_msg = "eh_entries is 0 but eh_depth is > 0";
> + goto corrupted;
> + }
> if (!ext4_valid_extent_entries(inode, eh, lblk, &pblk, depth)) {
> error_msg = "invalid extent entries";
> goto corrupted;
--
Jan Kara <[email protected]>
SUSE Labs, CR

2022-09-22 15:13:08

by Theodore Ts'o

[permalink] [raw]
Subject: Re: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0

On Mon, 22 Aug 2022 10:42:35 +0100, Luís Henriques wrote:
> When walking through an inode extents, the ext4_ext_binsearch_idx() function
> assumes that the extent header has been previously validated. However, there
> are no checks that verify that the number of entries (eh->eh_entries) is
> non-zero when depth is > 0. And this will lead to problems because the
> EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this:
>
> [ 135.245946] ------------[ cut here ]------------
> [ 135.247579] kernel BUG at fs/ext4/extents.c:2258!
> [ 135.249045] invalid opcode: 0000 [#1] PREEMPT SMP
> [ 135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4
> [ 135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
> [ 135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0
> [ 135.256475] Code:
> [ 135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246
> [ 135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023
> [ 135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c
> [ 135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c
> [ 135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024
> [ 135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000
> [ 135.272394] FS: 00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
> [ 135.274510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0
> [ 135.277952] Call Trace:
> [ 135.278635] <TASK>
> [ 135.279247] ? preempt_count_add+0x6d/0xa0
> [ 135.280358] ? percpu_counter_add_batch+0x55/0xb0
> [ 135.281612] ? _raw_read_unlock+0x18/0x30
> [ 135.282704] ext4_map_blocks+0x294/0x5a0
> [ 135.283745] ? xa_load+0x6f/0xa0
> [ 135.284562] ext4_mpage_readpages+0x3d6/0x770
> [ 135.285646] read_pages+0x67/0x1d0
> [ 135.286492] ? folio_add_lru+0x51/0x80
> [ 135.287441] page_cache_ra_unbounded+0x124/0x170
> [ 135.288510] filemap_get_pages+0x23d/0x5a0
> [ 135.289457] ? path_openat+0xa72/0xdd0
> [ 135.290332] filemap_read+0xbf/0x300
> [ 135.291158] ? _raw_spin_lock_irqsave+0x17/0x40
> [ 135.292192] new_sync_read+0x103/0x170
> [ 135.293014] vfs_read+0x15d/0x180
> [ 135.293745] ksys_read+0xa1/0xe0
> [ 135.294461] do_syscall_64+0x3c/0x80
> [ 135.295284] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> [...]

Applied, thanks!

[1/1] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0
commit: 29a5b8a137ac8eb410cc823653a29ac0e7b7e1b0

Best regards,
--
Theodore Ts'o <[email protected]>