In the Linux kernel, the following vulnerability has been resolved: smb/client: validate new EOF for zero range When FALLOC_FL_ZERO_RANGE

In the Linux kernel, the following vulnerability has been resolved:

smb/client: validate new EOF for zero range

When FALLOC_FL_ZERO_RANGE is used without FALLOC_FL_KEEP_SIZE,
smb3_zero_range() may extend EOF without checking RLIMIT_FSIZE, allowing
the file to grow beyond the caller's file-size limit.

Fix this by calling inode_newsize_ok() before sending the zero-range
request when the operation would extend EOF.

Reproducer, using a file on a CIFS mount:

 1bash -c '
 2        FILE=/mnt/cifs/repro
 3 
 4        trap "" SIGXFSZ
 5        ulimit -f 3072
 6 
 7        truncate -s 2M "$FILE"
 8        fallocate --zero-range -o 0 -l 4M "$FILE"
 9        echo "fallocate rc=$?"
10        stat -c "file size=%s" "$FILE"
11'

Before this change, the operation succeeds despite the 3 MiB limit:

 1fallocate rc=0
 2file size=4194304

After this change, fallocate fails and leaves the file at 2 MiB.