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Message-Id: <20230330092352.1186349-1-matthias.goergens@gmail.com>
Date: Thu, 30 Mar 2023 17:23:52 +0800
From: Matthias Goergens <matthias.goergens@...il.com>
To: musl@...ts.openwall.com
Cc: Matthias Goergens <matthias.goergens@...il.com>
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 a new version that incorporates suggestions by Szabolcs Nagy and rofl0r
The previous version had a helper function named `decode1` that decoded
a single escape. I implemented Szabolcs Nagy's extremely clever manual
inlining. However, I'm not completely sure that it's not too clever for
me. (It took me a while to understand why it works.)
---
src/misc/mntent.c | 85 +++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 78 insertions(+), 7 deletions(-)
diff --git a/src/misc/mntent.c b/src/misc/mntent.c
index d404fbe3..1c129579 100644
--- a/src/misc/mntent.c
+++ b/src/misc/mntent.c
@@ -1,8 +1,10 @@
+#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <mntent.h>
#include <errno.h>
#include <limits.h>
+#include "stdio_impl.h"
static char *internal_buf;
static size_t internal_bufsize;
@@ -20,6 +22,46 @@ int endmntent(FILE *f)
return 1;
}
+static char* decode(char* buf) {
+ assert(buf != NULL);
+ char* src = buf;
+ char* dest = buf;
+ while (1) {
+ char* next_src = __strchrnul(src, '\\');
+ int offset = next_src - src;
+ memmove(dest, src, offset);
+ src = next_src;
+ dest += offset;
+
+ if(*src == '\0') {
+ *dest = *src;
+ return buf;
+ }
+ assert (*src == '\\');
+ src++;
+
+ const char *replacements =
+ "\040" "040" "\0" // space
+ "\011" "011" "\0" // tab
+ "\012" "012" "\0" // newline
+ "\134" "134" "\0" // backslash
+ "\\" "\\" "\0"
+ // Fallback for unrecognized escape sequence,
+ // copy literally:
+ "\\" "";
+ while(1) {
+ char c = *replacements++;
+ size_t n = strlen(replacements);
+ if (strncmp(src, replacements, n) == 0) {
+ *dest++ = c;
+ src += n;
+ break;
+ }
+ replacements += n+1;
+ }
+ }
+}
+
struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int buflen)
{
int n[8], use_internal = (linebuf == SENTINEL);
@@ -55,10 +97,10 @@ 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 +111,41 @@ struct mntent *getmntent(FILE *f)
return getmntent_r(f, &mnt, SENTINEL, 0);
}
+static int escape_and_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 = fputs("\\040", f) < 0;
+ else if (c == '\011') // tab
+ error_occured = fputs("\\011", f) < 0;
+ else if (c == '\012') // newline
+ error_occured = fputs("\\012", f) < 0;
+ else if (c == '\\')
+ error_occured = fputs("\\\\", f) < 0;
+ else
+ error_occured = putc_unlocked(c, f) < 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;
+ FLOCK(f);
+ int error_occured =
+ escape_and_write_string(f, mnt->mnt_fsname)
+ || (0 > putc_unlocked('\t', f))
+ || escape_and_write_string(f, mnt->mnt_dir)
+ || (0 > putc_unlocked('\t', f))
+ || escape_and_write_string(f, mnt->mnt_type)
+ || (0 > putc_unlocked('\t', f))
+ || escape_and_write_string(f, mnt->mnt_opts)
+ || (0 > fprintf(f, "\t%d\t%d\n",
+ mnt->mnt_freq, mnt->mnt_passno));
+ FUNLOCK(f);
+ return error_occured;
}
char *hasmntopt(const struct mntent *mnt, const char *opt)
--
2.40.0
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