[PATCH v2 1/2] fs/squashfs: fix integer overflow in directory table allocation

sqfs_read_directory_table() allocates the directory table with
malloc(metablks_count * SQFS_METADATA_BLOCK_SIZE). metablks_count is an
int and SQFS_METADATA_BLOCK_SIZE is 8192, so the multiply is evaluated in
int and wraps for metablks_count >= 2^19. metablks_count comes from the
attacker-controlled superblock (sqfs_count_metablks() grows it by one per
2-byte metadata header), so a crafted image under-allocates the buffer
while the fill loop still writes metablks_count metadata blocks into it,
a heap out-of-bounds write. It is reached by listing or reading the image
(sqfsls / sqfsload). The position list allocation on the next line has the
same unchecked-multiply shape.

Size both allocations with __builtin_mul_overflow() and reject the image
on overflow, as the disk-read buffers earlier in the same function already
do. Set the error return when either allocation fails so the caller does
not proceed with a NULL directory table.

Fixes: c51006130370 ("fs/squashfs: new filesystem")
Signed-off-by: Shahriyar Jalayeri <[email protected]>
---
 fs/squashfs/sqfs.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
index 0768fc4a7b2..3aadcdd36ec 100644
--- a/fs/squashfs/sqfs.c
+++ b/fs/squashfs/sqfs.c
@@ -852,13 +852,28 @@ static int sqfs_read_directory_table(unsigned char **dir_table, u32 **pos_list)
 	if (metablks_count < 1)
 		goto out;
 
-	*dir_table = malloc(metablks_count * SQFS_METADATA_BLOCK_SIZE);
-	if (!*dir_table)
+	if (__builtin_mul_overflow(metablks_count, SQFS_METADATA_BLOCK_SIZE,
+				   &buf_size)) {
+		metablks_count = -1;
+		goto out;
+	}
+
+	*dir_table = malloc(buf_size);
+	if (!*dir_table) {
+		metablks_count = -1;
+		goto out;
+	}
+
+	if (__builtin_mul_overflow(metablks_count, sizeof(u32), &buf_size)) {
+		metablks_count = -1;
 		goto out;
+	}
 
-	*pos_list = malloc(metablks_count * sizeof(u32));
-	if (!*pos_list)
+	*pos_list = malloc(buf_size);
+	if (!*pos_list) {
+		metablks_count = -1;
 		goto out;
+	}
 
 	ret = sqfs_get_metablk_pos(*pos_list, dtb, table_offset,
 				   metablks_count);

-- 
2.43.0