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ext4: avoid arithemetic overflow that can trigger a BUG

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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
This commit is contained in:
Theodore Ts'o 2018-09-01 12:45:04 -04:00
parent 4d982e25d0
commit bcd8e91f98
2 changed files with 9 additions and 2 deletions
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3
fs/ext4/ext4.h
View file

@ -686,6 +686,9 @@ enum {
/* 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
*/

8
fs/ext4/inode.c
View file

@ -3412,12 +3412,16 @@ 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;
bool delalloc = false;
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 (flags & IOMAP_REPORT) {
if (ext4_has_inline_data(inode)) {