cygwin 3.5.4-1: lockf() aborts on overlap and does not fail on overflow

[Takashi Yano]

On Mon, 14 Oct 2024 15:36:02 +0200
Christian Franke wrote:
> Two possibly independent bugs found by 'stress-ng --lockf ...':
> 
> 1) lockf() may abort the process with api_fatal() if the new range 
> partly overlaps with two ranges previously locked by the same process.
> 
> 2) lockf() prints a warning on too many locks and returns success. It 
> should not print a warning and fail with ENOLCK instead.
> 
> Testcase for both:
> 
> $ uname -r
> 3.5.4-1.x86_64
> 
> $ cat locktest.c
> #include <fcntl.h>
> #include <stdio.h>
> #include <unistd.h>
> 
> static int lock_at(int fd, int off, int size)
> {
>    if (lseek(fd, off, SEEK_SET) < 0) {
>      perror("lseek"); return -1;
>    }
>    printf("\rlock %d-%d\n", off, off + size - 1); fflush(stdout);
>    if (lockf(fd, F_LOCK, size) < 0) {
>      perror("lock"); return -1;
>    }
>    return 0;
> }
> 
> int main(int argc, char **argv)
> {
>    int fd = open("locktest.tmp", O_RDWR|O_CREAT, 0666);
>    if (fd < 0) {
>      perror("open"); return 1;
>    }
> 
>    if (argc == 1) {
>      lock_at(fd, 0, 2);
>      lock_at(fd, 2, 2);
>      lock_at(fd, 1, 2);
>    }
>    else {
>      for (int i = 0; i < 914; i++)
>        if (lock_at(fd, i, 1))
>          return 1;
>    }
>    printf("\rdone\n");
>    return 0;
> }
> 
> $ gcc -o locktest locktest.c
> 
> $ ./locktest
> lock 0-1
> lock 2-3
> lock 1-2
>       1 [main] locktest 44864 C:\cygwin64\tmp\locktest.exe: \
>         *** fatal error - NtCreateEvent(lock): 0xC0000035\
>         Hangup
> 
> $ ./locktest loop
> lock 0-0
> lock 1-1
> lock 2-2
> lock 3-3
> ...
> lock 909-909
> lock 910-910
> lock 911-911
>        0 [main] locktest 44865 inode_t::get_all_locks_list: \
>          Warning, can't handle more than 910 locks per file.
> lock 912-912
>      727 [main] locktest 44865 inode_t::get_all_locks_list: \
>          Warning, can't handle more than 910 locks per file.
> lock 913-913
>     1329 [main] locktest 44865 inode_t::get_all_locks_list: \
>          Warning, can't handle more than 910 locks per file.
> done
> 
> There is possibly also an off-by-one error as the 912'th lockf() prints 
> the first warning.

Thanks for the report.
I looked into the problems, and considered how to fix them.

Could you please try the experimental patch attached?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>
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