[PATCH 0/2] ext4: Fix crash when adding entry to corrupted directory

[PATCH 0/2] ext4: Fix crash when adding entry to corrupted directory

[Jan Kara]

Hello,

two patches in this series try to fix a crash when adding directory entry to a
directory with corrupted h-tree. Since I don't have the filesystem image
causing the crash, I'm not sure what was the cause but the stacktrace suggests
we have corrupted one h-tree node while modifying another one so likely
there was a cycle created in the h-tree. This series checks for it and bails
out early.

								Honza

[PATCH 1/2] ext4: Verify dir block before splitting it

[Jan Kara]

Before splitting a directory block verify its directory entries are sane
so that the splitting code does not access memory it should not.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/namei.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 767b4bfe39c3..ca6ee9940599 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -277,9 +277,9 @@ static struct dx_frame *dx_probe(struct ext4_filename *fname,
 				 struct dx_hash_info *hinfo,
 				 struct dx_frame *frame);
 static void dx_release(struct dx_frame *frames);
-static int dx_make_map(struct inode *dir, struct ext4_dir_entry_2 *de,
-		       unsigned blocksize, struct dx_hash_info *hinfo,
-		       struct dx_map_entry map[]);
+static int dx_make_map(struct inode *dir, struct buffer_head *bh,
+		       struct dx_hash_info *hinfo,
+		       struct dx_map_entry *map_tail);
 static void dx_sort_map(struct dx_map_entry *map, unsigned count);
 static struct ext4_dir_entry_2 *dx_move_dirents(struct inode *dir, char *from,
 					char *to, struct dx_map_entry *offsets,
@@ -1249,15 +1249,23 @@ static inline int search_dirblock(struct buffer_head *bh,
  * Create map of hash values, offsets, and sizes, stored at end of block.
  * Returns number of entries mapped.
  */
-static int dx_make_map(struct inode *dir, struct ext4_dir_entry_2 *de,
-		       unsigned blocksize, struct dx_hash_info *hinfo,
+static int dx_make_map(struct inode *dir, struct buffer_head *bh,
+		       struct dx_hash_info *hinfo,
 		       struct dx_map_entry *map_tail)
 {
 	int count = 0;
-	char *base = (char *) de;
+	struct ext4_dir_entry_2 *de = (struct ext4_dir_entry_2 *)bh->b_data;
+	unsigned int buflen = bh->b_size;
+	char *base = bh->b_data;
 	struct dx_hash_info h = *hinfo;
 
-	while ((char *) de < base + blocksize) {
+	if (ext4_has_metadata_csum(dir->i_sb))
+		buflen -= sizeof(struct ext4_dir_entry_tail);
+
+	while ((char *) de < base + buflen) {
+		if (ext4_check_dir_entry(dir, NULL, de, bh, base, buflen,
+					 ((char *)de) - base))
+			return -EFSCORRUPTED;
 		if (de->name_len && de->inode) {
 			if (ext4_hash_in_dirent(dir))
 				h.hash = EXT4_DIRENT_HASH(de);
@@ -1270,7 +1278,6 @@ static int dx_make_map(struct inode *dir, struct ext4_dir_entry_2 *de,
 			count++;
 			cond_resched();
 		}
-		/* XXX: do we need to check rec_len == 0 case? -Chris */
 		de = ext4_next_entry(de, blocksize);
 	}
 	return count;
@@ -1943,8 +1950,11 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
 
 	/* create map in the end of data2 block */
 	map = (struct dx_map_entry *) (data2 + blocksize);
-	count = dx_make_map(dir, (struct ext4_dir_entry_2 *) data1,
-			     blocksize, hinfo, map);
+	count = dx_make_map(dir, *bh, hinfo, map);
+	if (count < 0) {
+		err = count;
+		goto journal_error;
+	}
 	map -= count;
 	dx_sort_map(map, count);
 	/* Ensure that neither split block is over half full */
-- 
2.34.1

[PATCH 2/2] ext4: Avoid cycles in directory h-tree

[Jan Kara]

A maliciously corrupted filesystem can contain cycles in the h-tree
stored inside a directory. That can easily lead to the kernel corrupting
tree nodes that were already verified under its hands while doing a node
split and consequently accessing unallocated memory. Fix the problem by
verifying traversed block numbers are unique.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/namei.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index ca6ee9940599..06441ad6104d 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -777,12 +777,14 @@ static struct dx_frame *
 dx_probe(struct ext4_filename *fname, struct inode *dir,
 	 struct dx_hash_info *hinfo, struct dx_frame *frame_in)
 {
-	unsigned count, indirect;
+	unsigned count, indirect, level, i;
 	struct dx_entry *at, *entries, *p, *q, *m;
 	struct dx_root *root;
 	struct dx_frame *frame = frame_in;
 	struct dx_frame *ret_err = ERR_PTR(ERR_BAD_DX_DIR);
 	u32 hash;
+	ext4_lblk_t block;
+	ext4_lblk_t blocks[EXT4_HTREE_LEVEL];
 
 	memset(frame_in, 0, EXT4_HTREE_LEVEL * sizeof(frame_in[0]));
 	frame->bh = ext4_read_dirblock(dir, 0, INDEX);
@@ -854,6 +856,8 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 	}
 
 	dxtrace(printk("Look up %x", hash));
+	level = 0;
+	blocks[0] = 0;
 	while (1) {
 		count = dx_get_count(entries);
 		if (!count || count > dx_get_limit(entries)) {
@@ -882,15 +886,27 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 			       dx_get_block(at)));
 		frame->entries = entries;
 		frame->at = at;
-		if (!indirect--)
+
+		block = dx_get_block(at);
+		for (i = 0; i <= level; i++) {
+			if (blocks[i] == block) {
+				ext4_warning_inode(dir,
+					"dx entry: tree cycle block %u points back to block %u",
+					blocks[level], block);
+				goto fail;
+			}
+		}
+		blocks[++level] = block;
+		if (level > indirect)
 			return frame;
 		frame++;
-		frame->bh = ext4_read_dirblock(dir, dx_get_block(at), INDEX);
+		frame->bh = ext4_read_dirblock(dir, block, INDEX);
 		if (IS_ERR(frame->bh)) {
 			ret_err = (struct dx_frame *) frame->bh;
 			frame->bh = NULL;
 			goto fail;
 		}
+
 		entries = ((struct dx_node *) frame->bh->b_data)->entries;
 
 		if (dx_get_limit(entries) != dx_node_limit(dir)) {
@@ -1278,7 +1294,7 @@ static int dx_make_map(struct inode *dir, struct buffer_head *bh,
 			count++;
 			cond_resched();
 		}
-		de = ext4_next_entry(de, blocksize);
+		de = ext4_next_entry(de, dir->i_sb->s_blocksize);
 	}
 	return count;
 }
-- 
2.34.1

Re: [PATCH 1/2] ext4: Verify dir block before splitting it

[Theodore Ts'o]

On Thu, Apr 28, 2022 at 08:31:37PM +0200, Jan Kara wrote:
> Before splitting a directory block verify its directory entries are sane
> so that the splitting code does not access memory it should not.

This commit fails to build due to an undefined variable.  It's fixed
with this hunk in the next patch, which needs to be brought back into
this commit:

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 5951e9bb348e..7286472e9558 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1278,7 +1278,7 @@ static int dx_make_map(struct inode *dir, struct buffer_head *bh,
 			count++;
 			cond_resched();
 		}
-		de = ext4_next_entry(de, blocksize);
+		de = ext4_next_entry(de, dir->i_sb->s_blocksize);
 	}
 	return count;
 }

I was thinking about folding in this change and apply the patch with
that change --- and I may yet do that --- but it looks like there's a
bigger problem with this patch series, which is that it's causing a
crash when running ext4/052 due to what appears to be a smashed stack.
More about that in the reply to patch 2/2 of this series....

						- Ted

Re: [PATCH 2/2] ext4: Avoid cycles in directory h-tree

[Theodore Ts'o]

On Thu, Apr 28, 2022 at 08:31:38PM +0200, Jan Kara wrote:
> A maliciously corrupted filesystem can contain cycles in the h-tree
> stored inside a directory. That can easily lead to the kernel corrupting
> tree nodes that were already verified under its hands while doing a node
> split and consequently accessing unallocated memory. Fix the problem by
> verifying traversed block numbers are unique.
> 
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>

When I tried applying this patch, I got this crash:

ext4/052 23s ... 	[19:28:41][    2.683407] run fstests ext4/052 at 2022-05-17 19:28:41
[    5.433672] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: dx_probe+0x629/0x630
[    5.434449] CPU: 0 PID: 2468 Comm: dirstress Not tainted 5.18.0-rc5-xfstests-00019-g204e6b4d4cc1 #610
[    5.435012] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[    5.435501] Call Trace:
[    5.435659]  <TASK>
[    5.435791]  dump_stack_lvl+0x34/0x44
[    5.436027]  panic+0x107/0x28f
[    5.436221]  ? dx_probe+0x629/0x630
[    5.436430]  __stack_chk_fail+0x10/0x10
[    5.436663]  dx_probe+0x629/0x630
[    5.436869]  ext4_dx_add_entry+0x54/0x700
[    5.437176]  ext4_add_entry+0x38d/0x4e0
[    5.437421]  ext4_add_nondir+0x2b/0xc0
[    5.437647]  ext4_symlink+0x1c5/0x390
[    5.437869]  vfs_symlink+0x184/0x220
[    5.438095]  do_symlinkat+0x7a/0x110
[    5.438313]  __x64_sys_symlink+0x38/0x40
[    5.438548]  do_syscall_64+0x38/0x90
[    5.438762]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[    5.439070] RIP: 0033:0x7f8137109a97
[    5.439285] Code: f0 ff ff 73 01 c3 48 8b 0d f6 d3 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 58 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d c9 d3 0c 00 f7 d8 64 89 01 48
[    5.440374] RSP: 002b:00007ffc514a2428 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
[    5.440820] RAX: ffffffffffffffda RBX: 0000000000035d4a RCX: 00007f8137109a97
[    5.441278] RDX: 0000000000000000 RSI: 00007ffc514a2450 RDI: 00007ffc514a2450
[    5.441734] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000013
[    5.442153] R10: 00007ffc514a21c2 R11: 0000000000000246 R12: 0000000000061a80
[    5.442571] R13: 0000000000000000 R14: 00007ffc514a2450 R15: 00007ffc514a2c50
[    5.442989]  </TASK>
[    5.443289] Kernel Offset: disabled
[    5.443517] Rebooting in 5 seconds..

Applying just the first patch series (plus the patch hunk from this
commit needed so that the first patch compiles) does not result in a
crash, so the problem is clearly with this change.

Looking more closely at ext4/052 which tests the large_dir feature,
and then looking at the patch, I suspect the fix which is needed
is:

> +	ext4_lblk_t blocks[EXT4_HTREE_LEVEL];

needs to be

	ext4_lblk_t blocks[EXT4_HTREE_LEVEL + 1];

Otherwise on large htree which is 3 levels deep, this

> +		blocks[++level] = block;

is going to end up smashing the stack.

Jan, do you agree?

							- Ted

Re: [PATCH 1/2] ext4: Verify dir block before splitting it

[Jan Kara]

On Tue 17-05-22 19:40:11, Theodore Ts'o wrote:
> On Thu, Apr 28, 2022 at 08:31:37PM +0200, Jan Kara wrote:
> > Before splitting a directory block verify its directory entries are sane
> > so that the splitting code does not access memory it should not.
> 
> This commit fails to build due to an undefined variable.  It's fixed
> with this hunk in the next patch, which needs to be brought back into
> this commit:
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 5951e9bb348e..7286472e9558 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1278,7 +1278,7 @@ static int dx_make_map(struct inode *dir, struct buffer_head *bh,
>  			count++;
>  			cond_resched();
>  		}
> -		de = ext4_next_entry(de, blocksize);
> +		de = ext4_next_entry(de, dir->i_sb->s_blocksize);
>  	}
>  	return count;
>  }
> 
> I was thinking about folding in this change and apply the patch with
> that change --- and I may yet do that --- but it looks like there's a
> bigger problem with this patch series, which is that it's causing a
> crash when running ext4/052 due to what appears to be a smashed stack.
> More about that in the reply to patch 2/2 of this series....

Yup, I'll fix that. Thanks for catching this.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 2/2] ext4: Avoid cycles in directory h-tree

[Jan Kara]

On Tue 17-05-22 19:55:47, Theodore Ts'o wrote:
> On Thu, Apr 28, 2022 at 08:31:38PM +0200, Jan Kara wrote:
> > A maliciously corrupted filesystem can contain cycles in the h-tree
> > stored inside a directory. That can easily lead to the kernel corrupting
> > tree nodes that were already verified under its hands while doing a node
> > split and consequently accessing unallocated memory. Fix the problem by
> > verifying traversed block numbers are unique.
> > 
> > CC: stable@vger.kernel.org
> > Signed-off-by: Jan Kara <jack@suse.cz>
> 
> When I tried applying this patch, I got this crash:
> 
> ext4/052 23s ... 	[19:28:41][    2.683407] run fstests ext4/052 at 2022-05-17 19:28:41
> [    5.433672] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: dx_probe+0x629/0x630
> [    5.434449] CPU: 0 PID: 2468 Comm: dirstress Not tainted 5.18.0-rc5-xfstests-00019-g204e6b4d4cc1 #610
> [    5.435012] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> [    5.435501] Call Trace:
> [    5.435659]  <TASK>
> [    5.435791]  dump_stack_lvl+0x34/0x44
> [    5.436027]  panic+0x107/0x28f
> [    5.436221]  ? dx_probe+0x629/0x630
> [    5.436430]  __stack_chk_fail+0x10/0x10
> [    5.436663]  dx_probe+0x629/0x630
> [    5.436869]  ext4_dx_add_entry+0x54/0x700
> [    5.437176]  ext4_add_entry+0x38d/0x4e0
> [    5.437421]  ext4_add_nondir+0x2b/0xc0
> [    5.437647]  ext4_symlink+0x1c5/0x390
> [    5.437869]  vfs_symlink+0x184/0x220
> [    5.438095]  do_symlinkat+0x7a/0x110
> [    5.438313]  __x64_sys_symlink+0x38/0x40
> [    5.438548]  do_syscall_64+0x38/0x90
> [    5.438762]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> [    5.439070] RIP: 0033:0x7f8137109a97
> [    5.439285] Code: f0 ff ff 73 01 c3 48 8b 0d f6 d3 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 58 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d c9 d3 0c 00 f7 d8 64 89 01 48
> [    5.440374] RSP: 002b:00007ffc514a2428 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
> [    5.440820] RAX: ffffffffffffffda RBX: 0000000000035d4a RCX: 00007f8137109a97
> [    5.441278] RDX: 0000000000000000 RSI: 00007ffc514a2450 RDI: 00007ffc514a2450
> [    5.441734] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000013
> [    5.442153] R10: 00007ffc514a21c2 R11: 0000000000000246 R12: 0000000000061a80
> [    5.442571] R13: 0000000000000000 R14: 00007ffc514a2450 R15: 00007ffc514a2c50
> [    5.442989]  </TASK>
> [    5.443289] Kernel Offset: disabled
> [    5.443517] Rebooting in 5 seconds..
> 
> Applying just the first patch series (plus the patch hunk from this
> commit needed so that the first patch compiles) does not result in a
> crash, so the problem is clearly with this change.

I was wondering why my testing didn't catch this and the reason was that my
test VM had a version of xfstests which had ext4/052 test but somehow the
'tests/ext4/group' file didn't contain that test (and a few other newer
ones) so it didn't get executed. Not sure how that broken group file got
there but anyway it's fixed now and indeed ext4/052 test crashes for me as
well.

> Looking more closely at ext4/052 which tests the large_dir feature,
> and then looking at the patch, I suspect the fix which is needed
> is:
> 
> > +	ext4_lblk_t blocks[EXT4_HTREE_LEVEL];
> 
> needs to be
> 
> 	ext4_lblk_t blocks[EXT4_HTREE_LEVEL + 1];
> 
> Otherwise on large htree which is 3 levels deep, this
> 
> > +		blocks[++level] = block;
> 
> is going to end up smashing the stack.
> 
> Jan, do you agree?

Yes, thanks for debugging this! But I'd prefer a fix like:

		if (++level > indirect)
			return frame;
		blocks[level] = block;

because the store of the leaf block into 'blocks' array is just bogus. I'll
send V2 with both the issues fixed.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

[PATCH 2/2] ext4: Avoid cycles in directory h-tree

[Jan Kara]

A maliciously corrupted filesystem can contain cycles in the h-tree
stored inside a directory. That can easily lead to the kernel corrupting
tree nodes that were already verified under its hands while doing a node
split and consequently accessing unallocated memory. Fix the problem by
verifying traversed block numbers are unique.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/namei.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 2a55f23e4524..2ca99f1569c0 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -777,12 +777,14 @@ static struct dx_frame *
 dx_probe(struct ext4_filename *fname, struct inode *dir,
 	 struct dx_hash_info *hinfo, struct dx_frame *frame_in)
 {
-	unsigned count, indirect;
+	unsigned count, indirect, level, i;
 	struct dx_entry *at, *entries, *p, *q, *m;
 	struct dx_root *root;
 	struct dx_frame *frame = frame_in;
 	struct dx_frame *ret_err = ERR_PTR(ERR_BAD_DX_DIR);
 	u32 hash;
+	ext4_lblk_t block;
+	ext4_lblk_t blocks[EXT4_HTREE_LEVEL];
 
 	memset(frame_in, 0, EXT4_HTREE_LEVEL * sizeof(frame_in[0]));
 	frame->bh = ext4_read_dirblock(dir, 0, INDEX);
@@ -854,6 +856,8 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 	}
 
 	dxtrace(printk("Look up %x", hash));
+	level = 0;
+	blocks[0] = 0;
 	while (1) {
 		count = dx_get_count(entries);
 		if (!count || count > dx_get_limit(entries)) {
@@ -882,15 +886,27 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 			       dx_get_block(at)));
 		frame->entries = entries;
 		frame->at = at;
-		if (!indirect--)
+
+		block = dx_get_block(at);
+		for (i = 0; i <= level; i++) {
+			if (blocks[i] == block) {
+				ext4_warning_inode(dir,
+					"dx entry: tree cycle block %u points back to block %u",
+					blocks[level], block);
+				goto fail;
+			}
+		}
+		if (++level > indirect)
 			return frame;
+		blocks[level] = block;
 		frame++;
-		frame->bh = ext4_read_dirblock(dir, dx_get_block(at), INDEX);
+		frame->bh = ext4_read_dirblock(dir, block, INDEX);
 		if (IS_ERR(frame->bh)) {
 			ret_err = (struct dx_frame *) frame->bh;
 			frame->bh = NULL;
 			goto fail;
 		}
+
 		entries = ((struct dx_node *) frame->bh->b_data)->entries;
 
 		if (dx_get_limit(entries) != dx_node_limit(dir)) {
-- 
2.35.3