2020-04-16 20:44:02

by Ritesh Harjani

Subject: [PATCHv2 1/1] ext4: Fix overflow case for map.m_len in ext4_iomap_begin_*

EXT4_MAX_LOGICAL_BLOCK - map.m_lblk + 1 in case when
map.m_lblk (offset) is 0 could overflow an unsigned int
and become 0.

Fix this.

Fixes: d3b6f23f7167 ("ext4: move ext4_fiemap to use iomap framework")
Reported-and-tested-by: [email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Ritesh Harjani <[email protected]>
---
@Jan,
I retained your Reviewed by, since there was no logic change, but just couple
of minor change - missed semicolon and tab space issue.

fs/ext4/inode.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e416096fc081..d9feaaad8ab8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3424,6 +3424,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
int ret;
struct ext4_map_blocks map;
u8 blkbits = inode->i_blkbits;
+ loff_t len;

if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
return -EINVAL;
@@ -3435,8 +3436,11 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
* Calculate the first and last logical blocks respectively.
*/
map.m_lblk = offset >> blkbits;
- map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
- EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
+ len = min_t(loff_t, (offset + length - 1) >> blkbits,
+ EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
+ if (len > EXT4_MAX_LOGICAL_BLOCK)
+ len = EXT4_MAX_LOGICAL_BLOCK;
+ map.m_len = len;

if (flags & IOMAP_WRITE)
ret = ext4_iomap_alloc(inode, &map, flags);
@@ -3524,6 +3528,7 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
bool delalloc = false;
struct ext4_map_blocks map;
u8 blkbits = inode->i_blkbits;
+ loff_t len;

if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
return -EINVAL;
@@ -3541,8 +3546,11 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
* Calculate the first and last logical block respectively.
*/
map.m_lblk = offset >> blkbits;
- map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
- EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
+ len = min_t(loff_t, (offset + length - 1) >> blkbits,
+ EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
+ if (len > EXT4_MAX_LOGICAL_BLOCK)
+ len = EXT4_MAX_LOGICAL_BLOCK;
+ map.m_len = len;

/*
* Fiemap callers may call for offset beyond s_bitmap_maxbytes.
--
2.21.0

2020-04-22 12:26:55

by Ritesh Harjani

Subject: Re: [PATCHv2 1/1] ext4: Fix overflow case for map.m_len in ext4_iomap_begin_*

NACK on this patch.

Even though this fixes syzcaller reproducer, still it seems the right
fix should be:-
1. To make EXT4_MAX_LOGICAL_BLOCK to 0xfffffffe
2. And also add fiemap_check_ranges() call in overlayfs.
This is because fiemap_check_ranges() takes care of truncating the
length parameter to max sb->s_maxbytes which underlying filesystem can
handle. This will be similar to how VFS calls for fiemap on underlying
FS.

Currently running xfstests on patches which implements above logic.

-ritesh

On 4/17/20 12:22 AM, Ritesh Harjani wrote:
> EXT4_MAX_LOGICAL_BLOCK - map.m_lblk + 1 in case when
> map.m_lblk (offset) is 0 could overflow an unsigned int
> and become 0.
>
> Fix this.
>
> Fixes: d3b6f23f7167 ("ext4: move ext4_fiemap to use iomap framework")
> Reported-and-tested-by: [email protected]
> Reviewed-by: Jan Kara <[email protected]>
> Signed-off-by: Ritesh Harjani <[email protected]>
> ---
> @Jan,
> I retained your Reviewed by, since there was no logic change, but just couple
> of minor change - missed semicolon and tab space issue.
>
> fs/ext4/inode.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e416096fc081..d9feaaad8ab8 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3424,6 +3424,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> int ret;
> struct ext4_map_blocks map;
> u8 blkbits = inode->i_blkbits;
> + loff_t len;
>
> if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
> return -EINVAL;
> @@ -3435,8 +3436,11 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> * Calculate the first and last logical blocks respectively.
> */
> map.m_lblk = offset >> blkbits;
> - map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> - EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> + len = min_t(loff_t, (offset + length - 1) >> blkbits,
> + EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> + if (len > EXT4_MAX_LOGICAL_BLOCK)
> + len = EXT4_MAX_LOGICAL_BLOCK;
> + map.m_len = len;
>
> if (flags & IOMAP_WRITE)
> ret = ext4_iomap_alloc(inode, &map, flags);
> @@ -3524,6 +3528,7 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
> bool delalloc = false;
> struct ext4_map_blocks map;
> u8 blkbits = inode->i_blkbits;
> + loff_t len;
>
> if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
> return -EINVAL;
> @@ -3541,8 +3546,11 @@ static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,
> * Calculate the first and last logical block respectively.
> */
> map.m_lblk = offset >> blkbits;
> - map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> - EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> + len = min_t(loff_t, (offset + length - 1) >> blkbits,
> + EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> + if (len > EXT4_MAX_LOGICAL_BLOCK)
> + len = EXT4_MAX_LOGICAL_BLOCK;
> + map.m_len = len;
>
> /*
> * Fiemap callers may call for offset beyond s_bitmap_maxbytes.
>