ext4: avoid arithemetic overflow that can trigger a BUG

commit bcd8e91f98c156f4b1ebcfacae675f9cfd962441 upstream.

A maliciously crafted file system can cause an overflow when the
results of a 64-bit calculation is stored into a 32-bit length
parameter.

https://bugzilla.kernel.org/show_bug.cgi?id=200623

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0abb30d19fa18b8fb463615ee785caf9f9d0a8db..c96778c39885b9cc2fd8634dfc756975fef07457 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -714,6 +714,9 @@ struct fsxattr {
 /* Max physical block we can address w/o extents */
 #define EXT4_MAX_BLOCK_FILE_PHYS       0xFFFFFFFF
 
+/* Max logical block we can support */
+#define EXT4_MAX_LOGICAL_BLOCK         0xFFFFFFFF
+
 /*
  * Structure of an inode on the disk
  */

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f9baa59de0e2083b7463d5a49bcd224ea26b8ca3..9808df52ceca6472a5e2e2e4d2269b9bd13a6109 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3407,11 +3407,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 {
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        unsigned int blkbits = inode->i_blkbits;
-       unsigned long first_block = offset >> blkbits;
-       unsigned long last_block = (offset + length - 1) >> blkbits;
+       unsigned long first_block, last_block;
        struct ext4_map_blocks map;
        int ret;
 
+       if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
+               return -EINVAL;
+       first_block = offset >> blkbits;
+       last_block = min_t(loff_t, (offset + length - 1) >> blkbits,
+                          EXT4_MAX_LOGICAL_BLOCK);
+
        if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
                return -ERANGE;