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--bind-try fails when the source is a bind mounted deleted file #811
Description
touch a b
mount --bind a b
bwrap --bind-try b /x --ro-bind / / echo ok1
rm a
bwrap --bind-try b /x --ro-bind / / echo ok2
alternate example, without root:
touch a b; bwrap --bind / / --ro-bind $PWD/a $PWD/b sh -c 'bwrap --bind-try b /x --ro-bind / / echo ok1; rm a && bwrap --bind-try b /x --ro-bind / / echo ok2'
expected behavior: ok1, ok2
actual behavior: ok1, bwrap: Can't bind mount /tmp/x/b on /x: Unable to mount source on destination: No such file or directory
trimmed example strace output:
[pid 30523] openat(AT_FDCWD</>, "/oldroot", O_RDONLY|O_NOCTTY|O_CLOEXEC|O_PATH) = 4</oldroot>
[pid 30523] openat2(4</oldroot>, "/tmp/x/b", {flags=O_RDONLY|O_PATH, resolve=RESOLVE_NO_MAGICLINKS|RESOLVE_IN_ROOT}, 24) = 5</oldroot/tmp/x/b>(deleted)
[pid 30523] close(4</oldroot>) = 0
[pid 30523] fstat(5</oldroot/tmp/x/b>(deleted), {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
[pid 30523] openat(AT_FDCWD</>, "/newroot", O_RDONLY|O_NOCTTY|O_CLOEXEC|O_PATH) = 4</newroot>
[pid 30523] openat2(4</newroot>, "/", {flags=O_RDONLY|O_DIRECTORY, resolve=RESOLVE_NO_MAGICLINKS|RESOLVE_IN_ROOT}, 24) = 6</newroot>
[pid 30523] close(4</newroot>) = 0
[pid 30523] openat(6</newroot>, "x", O_WRONLY|O_CREAT|O_EXCL|O_NOCTTY|O_NOFOLLOW|O_CLOEXEC, 0444) = 4</newroot/x>
[pid 30523] close(4</newroot/x>) = 0
[pid 30523] openat(6</newroot>, "x", O_RDONLY|O_NOFOLLOW|O_CLOEXEC|O_PATH) = 4</newroot/x>
[pid 30523] fstat(4</newroot/x>, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
[pid 30523] readlink("/proc/self/fd/4", "/newroot/x", 99) = 10
[pid 30523] mount("/proc/self/fd/5", "/proc/self/fd/4", NULL, MS_BIND|MS_REC|MS_SILENT, NULL) = -1 ENOENT (No such file or directory)
basically, the file exists in the sense that it can be opened and I/O performed, but cannot be bind-mounted from. unfortunately, it doesn't seem to be possible to work around with new mount API. I'm not sure whether it makes more sense to argue the case to kernel maintainers, or silently ignore this error in bubblewrap.
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