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From: Alyssa Ross <hi@alyssa.is>
To: musl@lists.openwall.com
Cc: Alyssa Ross <hi@alyssa.is>
Subject: [musl] [PATCH musl 3/3] mntent: fix parsing lines with optional fields
Date: Sat, 21 Aug 2021 08:54:20 +0000
Message-ID: <20210821085420.474615-4-hi@alyssa.is> (raw)
In-Reply-To: <20210821085420.474615-1-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


  parent reply	other threads:[~2021-08-21 18:16 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-21  8:54 [musl] [PATCH 0/3] " Alyssa Ross
2021-08-21  8:54 ` [musl] [PATCH libc-test 1/3] functional: add mntent test Alyssa Ross
2021-08-21  8:54 ` [musl] [PATCH libc-test 2/3] functional: add mntent test for single-field line Alyssa Ross
2021-08-21  8:54 ` Alyssa Ross [this message]
2021-08-27 15:27   ` [musl] [PATCH musl 3/3] mntent: fix parsing lines with optional fields Érico Nogueira
2021-08-27 16:49     ` Rich Felker
2021-08-27 16:59       ` Rich Felker

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