While zalloc() takes a size_t type, adding 1 to the le32 variable will overflow. A carefully crafted ext4 filesystem can exhibit an inode size of 0xffffffff and as consequence zalloc() will do a zero allocation.
Later in the function the inode size is again used for copying data. So an attacker can overwrite memory.
Avoid the overflow by using the __builtin_add_overflow() helper.
Signed-off-by: Richard Weinberger richard@nod.at --- fs/ext4/ext4_common.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c index 2ff0dca249..32364b72fb 100644 --- a/fs/ext4/ext4_common.c +++ b/fs/ext4/ext4_common.c @@ -2183,13 +2183,18 @@ static char *ext4fs_read_symlink(struct ext2fs_node *node) struct ext2fs_node *diro = node; int status; loff_t actread; + size_t alloc_size;
if (!diro->inode_read) { status = ext4fs_read_inode(diro->data, diro->ino, &diro->inode); if (status == 0) return NULL; } - symlink = zalloc(le32_to_cpu(diro->inode.size) + 1); + + if (__builtin_add_overflow(le32_to_cpu(diro->inode.size), 1, &alloc_size)) + return NULL; + + symlink = zalloc(alloc_size); if (!symlink) return NULL;