From: Darrick J. Wong <djwong@xxxxxxxxxx>
On closer examination of the lockfile code, there is still a fatal flaw
in the locking logic. This is born out by the fact that you can run:
# truncate -s 300m /tmp/a
# mkfs.ext2 /tmp/a
# fuse2fs -o kernel /tmp/a /mnt -o lockfile=/tmp/fuselock
# fuse2fs -o kernel /tmp/a /mnt -o lockfile=/tmp/fuselock
and the second mount attempt succeeds where it really shouldn't. This
is due to the use of fopen(..., "w"), because "w" means "truncate or
create". It does /not/ imply O_CREAT | O_EXCL, which fails if the file
already exists. Theoretically that could have been done with mode
string "wx", but that's a glibc extension.
Fix this by calling open() directly with the O_ modes that we want.
Cc: <linux-ext4@xxxxxxxxxxxxxxx> # v1.47.3-rc3
Fixes: e50fbaa4d156a6 ("fuse2fs: clean up the lockfile handling")
Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
misc/fuse2fs.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index b7201f7c8ed185..ff8d4668cee217 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -4473,11 +4473,15 @@ int main(int argc, char *argv[])
}
if (fctx.lockfile) {
- FILE *lockfile = fopen(fctx.lockfile, "w");
char *resolved;
+ int lockfd;
- if (!lockfile) {
- err = errno;
+ lockfd = open(fctx.lockfile, O_RDWR | O_CREAT | O_EXCL, 0400);
+ if (lockfd < 0) {
+ if (errno == EEXIST)
+ err = EWOULDBLOCK;
+ else
+ err = errno;
err_printf(&fctx, "%s: %s: %s\n", fctx.lockfile,
_("opening lockfile failed"),
strerror(err));
@@ -4485,7 +4489,7 @@ int main(int argc, char *argv[])
ret |= 32;
goto out;
}
- fclose(lockfile);
+ close(lockfd);
resolved = realpath(fctx.lockfile, NULL);
if (!resolved) {
