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Don't require mount point for a non-directory to be a regular file

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Previously, mounting a socket over the top of an existing socket
would fail, because create_file() opens it with creat():

    $ test -e /run/systemd/resolve/io.systemd.Resolve && echo exists
    exists
    $ bwrap \
      --bind / / \
      --bind /run/systemd/resolve/io.systemd.Resolve \
             /run/systemd/resolve/io.systemd.Resolve \
      /bin/true
    bwrap: Can't create file at /run/systemd/resolve/io.systemd.Resolve: No such device or address

Tolerate the file existing as any type that we will be able to mount
a non-directory onto.

Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie
2021-03-11 19:52:28 +00:00
parent dc4c266cc5
commit a00f39fc4e
2 changed files with 15 additions and 3 deletions
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9
utils.c
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@@ -448,9 +448,14 @@ ensure_file (const char *path,
/* We check this ahead of time, otherwise
the create file will fail in the read-only
case with EROFS instead of EEXIST */
case with EROFS instead of EEXIST.
We're trying to set up a mount point for a non-directory, so any
non-directory, non-symlink is acceptable - it doesn't necessarily
have to be a regular file. */
if (stat (path, &buf) == 0 &&
S_ISREG (buf.st_mode))
!S_ISDIR (buf.st_mode) &&
!S_ISLNK (buf.st_mode))
return 0;
if (create_file (path, mode, NULL) != 0 && errno != EEXIST)