Comment 4 for bug 1994079

Created attachment 303085
C source to reproduce the fallocate/SIGXFSZ issue

This is a corner case on 32 bit systems when using large file offsets, fallocate and setrlimit. Issue found on ext4, probably also on other file systems(?).

Setting the RLIMIT_FSIZE with setrlimit to 0xffffffff and then fallocating 1 or more bytes at the offset of 0xffffffff should make the fallocate fail with EFBIG and generate a SIGXFSZ signal. On 64 bit platforms this works, on 32 bit platforms such as i386 4.15 kernels through to linux 6.0 it fails to generate EFBIG errors and SIGXFSZ.

Attached is a test program to illustrate the problem. It sets the file size limit and allocates 1024 bytes at the boundary file size limit for 3 offsets:

On 64 bit systems we get the expected results:
got signal SIGXFSZ
offset: 65536 (0x10000), fallocate returned: -1
got signal SIGXFSZ
offset: 4294966271 (0xfffffbff), fallocate returned: -1
got signal SIGXFSZ
offset: 4294967295 (0xffffffff), fallocate returned: -1

On 32 bit systems the code fails on the 0xffffffff offset:

got signal SIGXFSZ
offset: 65536 (0x10000), fallocate returned: -1
got signal SIGXFSZ
offset: 4294966271 (0xfffffbff), fallocate returned: -1
offset: 4294967295 (0xffffffff), fallocate returned: 0

Attached is the reproducer.

I found this while developing a file limit boundary test case in stress-ng and discovered it breaks on all 32 bit kernels (armhf, i386, etc), even with recent 5.15 and 6.0 kernels.

attached is a simple reproducer