[musl] [PATCH musl 3/3] mntent: fix parsing lines with optional fields

[Alyssa Ross <hi@alyssa.is>]

According to fstab(5), the last two fields are optional, but this
wasn't accepted by Musl.  After this change, only the first field is
required, which matches Glibc's behaviour.

Using sscanf as before, it would have been impossible to differentiate
between 0 fields and 4 fields, because sscanf would have returned 0 in
both cases due to the use of assignment suppression and %n for the
string fields (which is important to avoid copying any strings).  So
instead, before calling sscanf, initialize every string to the empty
string, and then we can check which strings are empty afterwards to
know how many fields were matched.
---

We could also be stricter about it, and enforce that the first four
fields are present, since the man page says only the last two are
optional.  Doing that would be a simple change of checking for the
presence of mnt_opts instead of mnt_fsname at the end of my patch.

 src/misc/mntent.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/misc/mntent.c b/src/misc/mntent.c
index eabb8200..5a68f0b9 100644
--- a/src/misc/mntent.c
+++ b/src/misc/mntent.c
@@ -21,7 +21,8 @@ int endmntent(FILE *f)
 
 struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int buflen)
 {
-	int cnt, n[8], use_internal = (linebuf == SENTINEL);
+	int use_internal = (linebuf == SENTINEL);
+	size_t len, i, n[8];
 
 	mnt->mnt_freq = 0;
 	mnt->mnt_passno = 0;
@@ -39,10 +40,14 @@ struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int bufle
 			errno = ERANGE;
 			return 0;
 		}
-		cnt = sscanf(linebuf, " %n%*s%n %n%*s%n %n%*s%n %n%*s%n %d %d",
-			n, n+1, n+2, n+3, n+4, n+5, n+6, n+7,
-			&mnt->mnt_freq, &mnt->mnt_passno);
-	} while (cnt < 2 || linebuf[n[0]] == '#');
+
+		len = strlen(linebuf);
+		for (i = 0; i < sizeof n / sizeof *n; i++) n[i] = len;
+		if (sscanf(linebuf, " %n%*s%n %n%*s%n %n%*s%n %n%*s%n %d %d",
+			n, n+1, n+2, n+3, n+4, n+5, n+6, n+7,
+			&mnt->mnt_freq, &mnt->mnt_passno) == EOF && ferror(f))
+			return 0;
+	} while (linebuf[n[0]] == '#');
 
 	linebuf[n[1]] = 0;
 	linebuf[n[3]] = 0;
@@ -54,6 +60,9 @@ struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int bufle
 	mnt->mnt_type = linebuf+n[4];
 	mnt->mnt_opts = linebuf+n[6];
 
+	if (!*mnt->mnt_fsname)
+		return 0;
+
 	return mnt;
 }
 
-- 
2.32.0