Could anyone help to review this patch?
Thanks,
-Jeff
On 04/12/2013 06:26 PM, Jeff Liu wrote:
> From: Jie Liu <jeff.liu@xxxxxxxxxx>
>
> On 32-bit machine, the s_maxbytes is larger than the MAX_LFS_FILESIZE limits if CONFIG_LBDAF is
> not enabled. Hence it's possible to create a huge file via buffered-IO write with a given offset
> beyond this limitation. e.g.
>
> # block_size=4096
> # offset=$(((2**32 - 1) * $block_size))
> # xfs_io -f -c "pwrite $offset $block_size" /storage/test_file
>
> In this case, xfs_io will hang at the page writeback stage soon since the given offset would
> cause an overflow at xfs_vm_writepage():
>
> end_index = offset >> PAGE_CACHE_SHIFT;
> last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
> if (page->index >= end_index) {
> unsigned offset_into_page = offset & (PAGE_CACHE_SIZE - 1);
>
> /*
> * Just skip the page if it is fully outside i_size, e.g. due
> * to a truncate operation that is in progress.
> */
> if (page->index >= end_index + 1 || offset_into_page == 0) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> unlock_page(page);
> return 0;
> }
> end_index is unsigned long so that the max value is '2^32-1 = 4294967295', and it
> would be evaluated to the max value with the given offset(when writing the page offset
> up to s_max_bytes) for above test case. As a result, (page->index >= end_index + 1) is
> ok as (end_index + 1) is overflowed to ZERO.
>
> Actually, create a file as above on 32-bit machine should be failed with EFBIG error returned
> because there has strict check up at generic_write_checks() against the given offset with a
> *correct* s_max_bytes.
>
> This patch fix the s_max_bytes to MAX_LFS_FILESIZE if the pre-calculated value is greater
> than it.
>
> Reported-by: Michael L. Semon <mlsemon35@xxxxxxxxx>
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
>
> ---
> fs/xfs/xfs_super.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index ea341ce..0644d61 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -585,6 +585,7 @@ xfs_max_file_offset(
> {
> unsigned int pagefactor = 1;
> unsigned int bitshift = BITS_PER_LONG - 1;
> + __uint64_t offset;
>
> /* Figure out maximum filesize, on Linux this can depend on
> * the filesystem blocksize (on 32 bit platforms).
> @@ -610,7 +611,10 @@ xfs_max_file_offset(
> # endif
> #endif
>
> - return (((__uint64_t)pagefactor) << bitshift) - 1;
> + offset = (((__uint64_t)pagefactor) << bitshift) - 1;
> +
> + /* Check against VM & VFS exposed limits */
> + return (offset > MAX_LFS_FILESIZE) ? MAX_LFS_FILESIZE : offset;
> }
>
> xfs_agnumber_t
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