[musl] [PATCH] mntent: deal with escaped whitespace in mtab and fstab

["Matthias Görgens" <matthias.goergens@gmail.com>]

From ca1001f856e314b0ea9d0f3a5d7c88106f151c2e Mon Sep 17 00:00:00 2001
From: Matthias Goergens <matthias.goergens@gmail.com>
Date: Wed, 29 Mar 2023 16:17:49 +0800
Subject: [PATCH] mntent: deal with escaped whitespace in mtab and fstab

From glibc's documentation:

> Since fields in the mtab and fstab files are separated by whitespace,
> octal escapes are used to represent the characters space (\040),
> tab (\011), newline (\012), and backslash (\\) in those files when they
> occur in one of the four strings in a mntent structure. The
> routines addmntent() and getmntent() will convert from string
> representation to escaped representation and back. When converting
> from escaped representation, the sequence \134 is also converted to a
> backslash.

This fixes the issue reported in
https://www.openwall.com/lists/musl/2021/12/14/1

This is my first time contributing to musl.  Please point out any
mistakes you can find.

I am not quite sure I understand everything, and have also probably
gotten the style wrong?

Thanks!
---
src/misc/mntent.c | 71 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 64 insertions(+), 7 deletions(-)

diff --git a/src/misc/mntent.c b/src/misc/mntent.c
index d404fbe3..527acc01 100644
--- a/src/misc/mntent.c
+++ b/src/misc/mntent.c
@@ -20,6 +20,34 @@ int endmntent(FILE *f)
return 1;
}
+static inline int decode1(char** in_buf, char** out_buf, const char*
from, const char to) {
+ if(strncmp(from, *in_buf, strlen(from)) == 0) {
+ *(*out_buf)++ = to;
+ *in_buf += strlen(from);
+ return 1;
+ }
+ return 0;
+}
+
+static inline char* decode(char* buf) {
+ char* read_cursor = buf;
+ char* write_cursor = buf;
+ while(read_cursor && *read_cursor) {
+ // space
+ decode1(&read_cursor, &write_cursor, "\\040", '\040')
+ // tab
+ || decode1(&read_cursor, &write_cursor, "\\011", '\011')
+ // newline
+ || decode1(&read_cursor, &write_cursor, "\\012", '\012')
+ // backslash
+ || decode1(&read_cursor, &write_cursor, "\\134", '\134')
+ || decode1(&read_cursor, &write_cursor, "\\\\", '\\')
+ // default: copy char as is.
+ || (*write_cursor++ = *read_cursor++);
+ }
+ return buf;
+}
+
struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf,
int buflen)
{
int n[8], use_internal = (linebuf == SENTINEL);
@@ -55,10 +83,10 @@ struct mntent *getmntent_r(FILE *f, struct mntent
*mnt, char *linebuf, int bufle
linebuf[n[5]] = 0;
linebuf[n[7]] = 0;
- mnt->mnt_fsname = linebuf+n[0];
- mnt->mnt_dir = linebuf+n[2];
- mnt->mnt_type = linebuf+n[4];
- mnt->mnt_opts = linebuf+n[6];
+ mnt->mnt_fsname = decode(linebuf+n[0]);
+ mnt->mnt_dir = decode(linebuf+n[2]);
+ mnt->mnt_type = decode(linebuf+n[4]);
+ mnt->mnt_opts = decode(linebuf+n[6]);
return mnt;
}
@@ -69,12 +97,41 @@ struct mntent *getmntent(FILE *f)
return getmntent_r(f, &mnt, SENTINEL, 0);
}
+static inline int write_string(FILE *f, const char* str)
+{
+ char c;
+ int error_occured = 0;
+ while(str && !error_occured && (c = *str++) != 0) {
+ if(c == '\040') // space
+ error_occured = fprintf(f, "%s", "\\040") < 0;
+ else if (c == '\011') // tab
+ error_occured = fprintf(f, "%s", "\\011") < 0;
+ else if (c == '\012') // newline
+ error_occured = fprintf(f, "%s", "\\012") < 0;
+ else if (c == '\\')
+ error_occured = fprintf(f, "%s", "\\\\") < 0;
+ else
+ error_occured = fprintf(f, "%c", c) < 0;
+ }
+ return error_occured;
+}
+
int addmntent(FILE *f, const struct mntent *mnt)
{
if (fseek(f, 0, SEEK_END)) return 1;
- return fprintf(f, "%s\t%s\t%s\t%s\t%d\t%d\n",
- mnt->mnt_fsname, mnt->mnt_dir, mnt->mnt_type, mnt->mnt_opts,
- mnt->mnt_freq, mnt->mnt_passno) < 0;
+ flockfile(f);
+ int result =
+ write_string(f, mnt->mnt_fsname)
+ || (fprintf(f, "\t") < 0)
+ || write_string(f, mnt->mnt_dir)
+ || (fprintf(f, "\t") < 0)
+ || write_string(f, mnt->mnt_type)
+ || (fprintf(f, "\t") < 0)
+ || write_string(f, mnt->mnt_opts)
+ || (fprintf(f, "\t%d\t%d\n",
+ mnt->mnt_freq, mnt->mnt_passno) < 0);
+ funlockfile(f);
+ return result;
}
char *hasmntopt(const struct mntent *mnt, const char *opt)
-- 
2.40.0