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Message-ID: <4ddc754a.rUkSC+Fh8Nx3g9+6%phillip@lougher.demon.co.uk>
Date: Wed, 25 May 2011 04:19:38 +0100
From: Phillip Lougher <phillip@...gher.demon.co.uk>
To: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 4/7] Squashfs: add sanity checks to id reading at mount
time
Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc. One of these is due to a corrupted superblock no_ids field.
Fix this by checking that the number of bytes to be read (and allocated)
does not extend into the next filesystem structure.
Also add a couple of other sanity checks of the mount-time id table
structures.
Signed-off-by: Phillip Lougher <phillip@...gher.demon.co.uk>
---
fs/squashfs/id.c | 30 ++++++++++++++++++++++++++++--
fs/squashfs/squashfs.h | 2 +-
fs/squashfs/super.c | 10 +++++++---
fs/squashfs/xattr.h | 1 +
4 files changed, 37 insertions(+), 6 deletions(-)
diff --git a/fs/squashfs/id.c b/fs/squashfs/id.c
index 2fdac67..8650cb0 100644
--- a/fs/squashfs/id.c
+++ b/fs/squashfs/id.c
@@ -66,11 +66,37 @@ int squashfs_get_id(struct super_block *sb, unsigned int index,
* Read uncompressed id lookup table indexes from disk into memory
*/
__le64 *squashfs_read_id_index_table(struct super_block *sb,
- u64 id_table_start, unsigned short no_ids)
+ u64 id_table_start, u64 next_table, unsigned short no_ids)
{
unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids);
+ __le64 *table;
TRACE("In read_id_index_table, length %d\n", length);
- return squashfs_read_table(sb, id_table_start, length);
+ /* Sanity check values */
+
+ /* there should always be at least one id */
+ if (no_ids == 0)
+ return ERR_PTR(-EINVAL);
+
+ /*
+ * length bytes should not extend into the next table - this check
+ * also traps instances where id_table_start is incorrectly larger
+ * than the next table start
+ */
+ if (id_table_start + length > next_table)
+ return ERR_PTR(-EINVAL);
+
+ table = squashfs_read_table(sb, id_table_start, length);
+
+ /*
+ * table[0] points to the first id lookup table metadata block, this
+ * should be less than id_table_start
+ */
+ if (table[0] >= id_table_start) {
+ kfree(table);
+ return ERR_PTR(-EINVAL);
+ }
+
+ return table;
}
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index d622e84..0e3d220 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -61,7 +61,7 @@ extern __le64 *squashfs_read_fragment_index_table(struct super_block *,
/* id.c */
extern int squashfs_get_id(struct super_block *, unsigned int, unsigned int *);
-extern __le64 *squashfs_read_id_index_table(struct super_block *, u64,
+extern __le64 *squashfs_read_id_index_table(struct super_block *, u64, u64,
unsigned short);
/* inode.c */
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 401cc8c..8f5f278 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -83,7 +83,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
long long root_inode;
unsigned short flags;
unsigned int fragments;
- u64 lookup_table_start, xattr_id_table_start;
+ u64 lookup_table_start, xattr_id_table_start, next_table;
int err;
TRACE("Entered squashfs_fill_superblock\n");
@@ -217,8 +217,10 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
/* Handle xattrs */
sb->s_xattr = squashfs_xattr_handlers;
xattr_id_table_start = le64_to_cpu(sblk->xattr_id_table_start);
- if (xattr_id_table_start == SQUASHFS_INVALID_BLK)
+ if (xattr_id_table_start == SQUASHFS_INVALID_BLK) {
+ next_table = msblk->bytes_used;
goto allocate_id_index_table;
+ }
/* Allocate and read xattr id lookup table */
msblk->xattr_id_table = squashfs_read_xattr_id_table(sb,
@@ -230,11 +232,13 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
if (err != -ENOTSUPP)
goto failed_mount;
}
+ next_table = msblk->xattr_table;
allocate_id_index_table:
/* Allocate and read id index table */
msblk->id_table = squashfs_read_id_index_table(sb,
- le64_to_cpu(sblk->id_table_start), le16_to_cpu(sblk->no_ids));
+ le64_to_cpu(sblk->id_table_start), next_table,
+ le16_to_cpu(sblk->no_ids));
if (IS_ERR(msblk->id_table)) {
ERROR("unable to read id index table\n");
err = PTR_ERR(msblk->id_table);
diff --git a/fs/squashfs/xattr.h b/fs/squashfs/xattr.h
index b634efc..9b3dd6c 100644
--- a/fs/squashfs/xattr.h
+++ b/fs/squashfs/xattr.h
@@ -31,6 +31,7 @@ static inline __le64 *squashfs_read_xattr_id_table(struct super_block *sb,
u64 start, u64 *xattr_table_start, int *xattr_ids)
{
ERROR("Xattrs in filesystem, these will be ignored\n");
+ *xattr_table_start = start;
return ERR_PTR(-ENOTSUPP);
}
--
1.7.1
--
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