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checkpath: use O_PATH when available #244

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Dec 2, 2018
Merged

checkpath: use O_PATH when available #244

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44 changes: 41 additions & 3 deletions src/rc/checkpath.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,9 +16,11 @@
* except according to the terms contained in the LICENSE file.
*/

#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
Expand Down Expand Up @@ -69,6 +71,37 @@ const char * const longopts_help[] = {
};
const char *usagestring = NULL;

/* On Linux, fchmod() returns EBADF when passed a file descriptor opened
* with O_PATH. Use chmod() on /proc/self/fd as a workaround. */
static int fchmod_opath(int fd, mode_t mode)
{
#ifdef O_PATH
/* A 64-bit int will result in a maximum path length of 35 characters. */
char path[35];

/* Maybe we will have 128-bit ints someday. */
assert(sizeof(int) <= 8);

if (sprintf(path, "/proc/self/fd/%d", fd) < 0)
return -1;

return chmod(path, mode);
#else
return fchmod(fd, mode);
#endif
}

/* On Linux, fchown() returns EBADF when passed a file descriptor opened
* with O_PATH. fchownat() does not exhibit this flaw. */
static int fchown_opath(int fd, uid_t uid, gid_t gid)
{
#ifdef O_PATH
return fchownat(fd, "", uid, gid, AT_EMPTY_PATH);
#else
return fchown(fd, uid, gid);
#endif
}

static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
inode_t type, bool trunc, bool chowner, bool selinux_on)
{
Expand All @@ -82,14 +115,19 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,

memset(&st, 0, sizeof(st));
flags = O_CREAT|O_NDELAY|O_WRONLY|O_NOCTTY;
readflags = O_NDELAY|O_NOCTTY|O_RDONLY;
readflags = O_NDELAY|O_NOCTTY;
#ifdef O_CLOEXEC
flags |= O_CLOEXEC;
readflags |= O_CLOEXEC;
#endif
#ifdef O_NOFOLLOW
flags |= O_NOFOLLOW;
readflags |= O_NOFOLLOW;
#endif
#ifdef O_PATH
readflags |= O_PATH;
#else
readflags |= O_RDONLY;
#endif
if (trunc)
flags |= O_TRUNC;
Expand Down Expand Up @@ -177,7 +215,7 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
return -1;
}
einfo("%s: correcting mode", path);
if (fchmod(readfd, mode)) {
if (fchmod_opath(readfd, mode)) {
eerror("%s: chmod: %s", applet, strerror(errno));
close(readfd);
return -1;
Expand All @@ -196,7 +234,7 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
return -1;
}
einfo("%s: correcting owner", path);
if (fchown(readfd, uid, gid)) {
if (fchown_opath(readfd, uid, gid)) {
eerror("%s: chown: %s", applet, strerror(errno));
close(readfd);
return -1;
Expand Down