From: Phillip Lougher phillip@squashfs.org.uk
commit f37aa4c7366e23f91b81d00bafd6a7ab54e4a381 upstream.
Sysbot has reported a number of "slab-out-of-bounds reads" and "use-after-free read" errors which has been identified as being caused by a corrupted index value read from the inode. This could be because the metadata block is uncompressed, or because the "compression" bit has been corrupted (turning a compressed block into an uncompressed block).
This patch adds additional sanity checks to detect this, and the following corruption.
1. It checks against corruption of the ids count. This can either lead to a larger table to be read, or a smaller than expected table to be read.
In the case of a too large ids count, this would often have been trapped by the existing sanity checks, but this patch introduces a more exact check, which can identify too small values.
2. It checks the contents of the index table for corruption.
Link: https://lkml.kernel.org/r/20210204130249.4495-3-phillip@squashfs.org.uk Signed-off-by: Phillip Lougher phillip@squashfs.org.uk Reported-by: syzbot+b06d57ba83f604522af2@syzkaller.appspotmail.com Reported-by: syzbot+c021ba012da41ee9807c@syzkaller.appspotmail.com Reported-by: syzbot+5024636e8b5fd19f0f19@syzkaller.appspotmail.com Reported-by: syzbot+bcbc661df46657d0fa4f@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/squashfs/id.c | 40 ++++++++++++++++++++++++++++-------- fs/squashfs/squashfs_fs_sb.h | 1 + fs/squashfs/super.c | 6 +++--- fs/squashfs/xattr.h | 10 ++++++++- 4 files changed, 45 insertions(+), 12 deletions(-)
diff --git a/fs/squashfs/id.c b/fs/squashfs/id.c index d38ea3dab9515..8ccc0e3f6ea5a 100644 --- a/fs/squashfs/id.c +++ b/fs/squashfs/id.c @@ -48,10 +48,15 @@ int squashfs_get_id(struct super_block *sb, unsigned int index, struct squashfs_sb_info *msblk = sb->s_fs_info; int block = SQUASHFS_ID_BLOCK(index); int offset = SQUASHFS_ID_BLOCK_OFFSET(index); - u64 start_block = le64_to_cpu(msblk->id_table[block]); + u64 start_block; __le32 disk_id; int err;
+ if (index >= msblk->ids) + return -EINVAL; + + start_block = le64_to_cpu(msblk->id_table[block]); + err = squashfs_read_metadata(sb, &disk_id, &start_block, &offset, sizeof(disk_id)); if (err < 0) @@ -69,7 +74,10 @@ __le64 *squashfs_read_id_index_table(struct super_block *sb, u64 id_table_start, u64 next_table, unsigned short no_ids) { unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids); + unsigned int indexes = SQUASHFS_ID_BLOCKS(no_ids); + int n; __le64 *table; + u64 start, end;
TRACE("In read_id_index_table, length %d\n", length);
@@ -80,20 +88,36 @@ __le64 *squashfs_read_id_index_table(struct super_block *sb, 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 + * The computed size of the index table (length bytes) should exactly + * match the table start and end points */ - if (id_table_start + length > next_table) + if (length != (next_table - id_table_start)) return ERR_PTR(-EINVAL);
table = squashfs_read_table(sb, id_table_start, length); + if (IS_ERR(table)) + return table;
/* - * table[0] points to the first id lookup table metadata block, this - * should be less than id_table_start + * table[0], table[1], ... table[indexes - 1] store the locations + * of the compressed id blocks. Each entry should be less than + * the next (i.e. table[0] < table[1]), and the difference between them + * should be SQUASHFS_METADATA_SIZE or less. table[indexes - 1] + * should be less than id_table_start, and again the difference + * should be SQUASHFS_METADATA_SIZE or less */ - if (!IS_ERR(table) && le64_to_cpu(table[0]) >= id_table_start) { + for (n = 0; n < (indexes - 1); n++) { + start = le64_to_cpu(table[n]); + end = le64_to_cpu(table[n + 1]); + + if (start >= end || (end - start) > SQUASHFS_METADATA_SIZE) { + kfree(table); + return ERR_PTR(-EINVAL); + } + } + + start = le64_to_cpu(table[indexes - 1]); + if (start >= id_table_start || (id_table_start - start) > SQUASHFS_METADATA_SIZE) { kfree(table); return ERR_PTR(-EINVAL); } diff --git a/fs/squashfs/squashfs_fs_sb.h b/fs/squashfs/squashfs_fs_sb.h index ef69c31947bf8..5234c19a0eabc 100644 --- a/fs/squashfs/squashfs_fs_sb.h +++ b/fs/squashfs/squashfs_fs_sb.h @@ -77,5 +77,6 @@ struct squashfs_sb_info { unsigned int inodes; unsigned int fragments; int xattr_ids; + unsigned int ids; }; #endif diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c index 40e657386fa52..728b2d72f3f07 100644 --- a/fs/squashfs/super.c +++ b/fs/squashfs/super.c @@ -176,6 +176,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent) msblk->directory_table = le64_to_cpu(sblk->directory_table_start); msblk->inodes = le32_to_cpu(sblk->inodes); msblk->fragments = le32_to_cpu(sblk->fragments); + msblk->ids = le16_to_cpu(sblk->no_ids); flags = le16_to_cpu(sblk->flags);
TRACE("Found valid superblock on %pg\n", sb->s_bdev); @@ -187,7 +188,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent) TRACE("Block size %d\n", msblk->block_size); TRACE("Number of inodes %d\n", msblk->inodes); TRACE("Number of fragments %d\n", msblk->fragments); - TRACE("Number of ids %d\n", le16_to_cpu(sblk->no_ids)); + TRACE("Number of ids %d\n", msblk->ids); TRACE("sblk->inode_table_start %llx\n", msblk->inode_table); TRACE("sblk->directory_table_start %llx\n", msblk->directory_table); TRACE("sblk->fragment_table_start %llx\n", @@ -244,8 +245,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent) 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), next_table, - le16_to_cpu(sblk->no_ids)); + le64_to_cpu(sblk->id_table_start), next_table, msblk->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 afe70f815e3de..86b0a0073e51f 100644 --- a/fs/squashfs/xattr.h +++ b/fs/squashfs/xattr.h @@ -30,8 +30,16 @@ extern int squashfs_xattr_lookup(struct super_block *, unsigned int, int *, static inline __le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start, u64 *xattr_table_start, int *xattr_ids) { + struct squashfs_xattr_id_table *id_table; + + id_table = squashfs_read_table(sb, start, sizeof(*id_table)); + if (IS_ERR(id_table)) + return (__le64 *) id_table; + + *xattr_table_start = le64_to_cpu(id_table->xattr_table_start); + kfree(id_table); + ERROR("Xattrs in filesystem, these will be ignored\n"); - *xattr_table_start = start; return ERR_PTR(-ENOTSUPP); }