From: Phillip Lougher <phillip@xxxxxxxxxxxxxxx> Subject: squashfs: add more sanity checks in xattr id lookup Sysbot has reported a warning where a kmalloc() attempt exceeds the maximum limit. This has been identified as corruption of the xattr_ids count when reading the xattr id lookup table. This patch adds a number of additional sanity checks to detect this corruption and others. 1. It checks for a corrupted xattr index 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 would cause an out of bounds read. 2. It checks against corruption of the xattr_ids count. This can either lead to the above kmalloc failure, or a smaller than expected table to be read. 3. It checks the contents of the index table for corruption. [phillip@xxxxxxxxxxxxxxx: fix checkpatch issue] Link: https://lkml.kernel.org/r/270245655.754655.1612770082682@xxxxxxxxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20210204130249.4495-5-phillip@xxxxxxxxxxxxxxx Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx> Reported-by: syzbot+2ccea6339d368360800d@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/squashfs/xattr_id.c | 66 +++++++++++++++++++++++++++++++++------ 1 file changed, 57 insertions(+), 9 deletions(-) --- a/fs/squashfs/xattr_id.c~squashfs-add-more-sanity-checks-in-xattr-id-lookup +++ a/fs/squashfs/xattr_id.c @@ -31,10 +31,15 @@ int squashfs_xattr_lookup(struct super_b struct squashfs_sb_info *msblk = sb->s_fs_info; int block = SQUASHFS_XATTR_BLOCK(index); int offset = SQUASHFS_XATTR_BLOCK_OFFSET(index); - u64 start_block = le64_to_cpu(msblk->xattr_id_table[block]); + u64 start_block; struct squashfs_xattr_id id; int err; + if (index >= msblk->xattr_ids) + return -EINVAL; + + start_block = le64_to_cpu(msblk->xattr_id_table[block]); + err = squashfs_read_metadata(sb, &id, &start_block, &offset, sizeof(id)); if (err < 0) @@ -50,13 +55,17 @@ int squashfs_xattr_lookup(struct super_b /* * Read uncompressed xattr id lookup table indexes from disk into memory */ -__le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start, +__le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 table_start, u64 *xattr_table_start, int *xattr_ids) { - unsigned int len; + struct squashfs_sb_info *msblk = sb->s_fs_info; + unsigned int len, indexes; struct squashfs_xattr_id_table *id_table; + __le64 *table; + u64 start, end; + int n; - id_table = squashfs_read_table(sb, start, sizeof(*id_table)); + id_table = squashfs_read_table(sb, table_start, sizeof(*id_table)); if (IS_ERR(id_table)) return (__le64 *) id_table; @@ -70,13 +79,52 @@ __le64 *squashfs_read_xattr_id_table(str if (*xattr_ids == 0) return ERR_PTR(-EINVAL); - /* xattr_table should be less than start */ - if (*xattr_table_start >= start) + len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids); + indexes = SQUASHFS_XATTR_BLOCKS(*xattr_ids); + + /* + * The computed size of the index table (len bytes) should exactly + * match the table start and end points + */ + start = table_start + sizeof(*id_table); + end = msblk->bytes_used; + + if (len != (end - start)) return ERR_PTR(-EINVAL); - len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids); + table = squashfs_read_table(sb, start, len); + if (IS_ERR(table)) + return table; + + /* table[0], table[1], ... table[indexes - 1] store the locations + * of the compressed xattr 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 table_start, and again the difference + * shouls be SQUASHFS_METADATA_SIZE or less. + * + * Finally xattr_table_start should be less than table[0]. + */ + 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 >= table_start || (table_start - start) > SQUASHFS_METADATA_SIZE) { + kfree(table); + return ERR_PTR(-EINVAL); + } - TRACE("In read_xattr_index_table, length %d\n", len); + if (*xattr_table_start >= le64_to_cpu(table[0])) { + kfree(table); + return ERR_PTR(-EINVAL); + } - return squashfs_read_table(sb, start + sizeof(*id_table), len); + return table; } _
