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__readlink_chk, __readlinkat_chk: properly pass buffer length #115

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__readlink_chk, __readlinkat_chk: properly pass buffer length #115

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8 changes: 7 additions & 1 deletion src/__readlink_chk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@
#define _FORTIFY_SOURCE 2
#include <stddef.h>
#include <unistd.h>
#include <stdio.h>
#include "libfakechroot.h"


Expand All @@ -41,7 +42,12 @@ wrapper(__readlink_chk, ssize_t, (const char * path, char * buf, size_t bufsiz,
debug("__readlink_chk(\"%s\", &buf, %zd, %zd)", path, bufsiz, buflen);
expand_chroot_path(path);

if ((linksize = nextcall(__readlink_chk)(path, tmp, FAKECHROOT_PATH_MAX-1, buflen)) == -1) {
if (__builtin_expect(!!(bufsiz > buflen), 0)) {

@josch josch Nov 27, 2023

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why the double exclamation mark? bufsiz > buflen is already a boolean

printf("readlink: prevented write past end of buffer\n");

@josch josch Nov 27, 2023

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why the printf to stdout? at most there is a print to stderr done in the rest of the codebase

exit(-1);

@josch josch Nov 27, 2023

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why the exit? why not just return failure?

@vt-alt vt-alt Dec 13, 2023

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Because _chk functions should exit on overflow. Actually __chk_fail should be called (similar to __realpath_chk).
https://refspecs.linuxbase.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/libc---readlink-chk-1.html

}

if ((linksize = nextcall(__readlink_chk)(path, tmp, FAKECHROOT_PATH_MAX-1, FAKECHROOT_PATH_MAX-1)) == -1) {
return -1;
}
tmp[linksize] = '\0';
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8 changes: 7 additions & 1 deletion src/__readlinkat_chk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#define _FORTIFY_SOURCE 2
#include <stddef.h>
#include <unistd.h>
#include <stdio.h>
#include "libfakechroot.h"


Expand All @@ -42,7 +43,12 @@ wrapper(__readlinkat_chk, ssize_t, (int dirfd, const char * path, char * buf, si
debug("__readlinkat_chk(%d, \"%s\", &buf, %zd, %zd)", dirfd, path, bufsiz, buflen);
expand_chroot_path_at(dirfd, path);

if ((linksize = nextcall(__readlinkat_chk)(dirfd, path, tmp, FAKECHROOT_PATH_MAX-1, buflen)) == -1) {
if (__builtin_expect(!!(bufsiz > buflen), 0)) {
printf("readlinkat: prevented write past end of buffer\n");
exit(-1);
}

if ((linksize = nextcall(__readlinkat_chk)(dirfd, path, tmp, FAKECHROOT_PATH_MAX-1, FAKECHROOT_PATH_MAX-1)) == -1) {
return -1;
}
tmp[linksize] = '\0';
Expand Down