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Refactor: move read_symlink() from log.c to os.c

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This commit is contained in:
Andrew Bettison 2013-02-25 15:25:53 +10:30
parent 1e61e7a02f
commit 5518859b66
3 changed files with 48 additions and 42 deletions
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43
log.c
View File

@ -36,6 +36,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#include "log.h"
#include "net.h"
#include "os.h"
#include "conf.h"
#include "str.h"
#include "strbuf.h"
@ -303,48 +304,6 @@ int logDump(int level, struct __sourceloc whence, char *name, const unsigned cha
return 0;
}
/* Read the symbolic link into the supplied buffer and add a terminating nul. Return -1 if the
* buffer is too short to hold the link content and the nul. If readlink(2) returns an error, then
* logs it and returns -1. Otherwise, returns the number of bytes read, including the terminating
* nul, ie, returns what readlink(2) returns plus one. If the 'len' argument is given as zero, then
* returns the number of bytes that would be read, by calling lstat(2) instead of readlink(2), plus
* one for the terminating nul. Beware of the following race condition: a symbolic link may be
* altered between calling the lstat(2) and readlink(2), so the following apparently overflow-proof
* code may still fail from a buffer overflow in the second call to read_symlink():
*
* char *readlink_malloc(const char *path) {
* ssize_t len = read_symlink(path, NULL, 0);
* if (len == -1)
* return NULL;
* char *buf = malloc(len);
* if (buf == NULL)
* return NULL;
* if (read_symlink(path, buf, len) == -1) {
* free(buf);
* return NULL;
* }
* return buf;
* }
*
* @author Andrew Bettison <andrew@servalproject.com>
*/
ssize_t read_symlink(const char *path, char *buf, size_t len)
{
if (len == 0) {
struct stat stat;
if (lstat(path, &stat) == -1)
return WHYF_perror("lstat(%s)", path);
return stat.st_size;
}
ssize_t nr = readlink(path, buf, len);
if (nr == -1)
return WHYF_perror("readlink(%s)", path);
if (nr >= len)
return WHYF("buffer overrun from readlink(%s, len=%lu)", path, (unsigned long) len);
buf[nr] = '\0';
return nr;
}
ssize_t get_self_executable_path(char *buf, size_t len)
{
#if defined(linux)

17
os.c
View File

@ -140,3 +140,20 @@ time_ms_t sleep_ms(time_ms_t milliseconds)
FATALF_perror("nanosleep(tv_sec=%ld, tv_nsec=%ld)", delay.tv_sec, delay.tv_nsec);
return remain.tv_sec * 1000 + remain.tv_nsec / 1000000;
}
ssize_t read_symlink(const char *path, char *buf, size_t len)
{
if (len == 0) {
struct stat stat;
if (lstat(path, &stat) == -1)
return WHYF_perror("lstat(%s)", path);
return stat.st_size;
}
ssize_t nr = readlink(path, buf, len);
if (nr == -1)
return WHYF_perror("readlink(%s)", path);
if (nr >= len)
return WHYF("buffer overrun from readlink(%s, len=%lu)", path, (unsigned long) len);
buf[nr] = '\0';
return nr;
}

30
os.h
View File

@ -75,4 +75,34 @@ int mkdirsn(const char *path, size_t len, mode_t mode);
void srandomdev();
int urandombytes(unsigned char *buf, unsigned long long len);
/* Read the symbolic link into the supplied buffer and add a terminating nul.
* Logs an ERROR and returns -1 if the buffer is too short to hold the link
* content and the terminating nul. If readlink(2) returns an error, then logs
* an ERROR and returns -1. Otherwise, returns the number of bytes read,
* including the terminating nul, ie, returns what readlink(2) returns plus
* one. If the 'len' argument is given as zero, then returns the number of
* bytes that would be read, by calling lstat(2) instead of readlink(2), plus
* one for the terminating nul. Beware of the following race condition: a
* symbolic link may be altered between calling the lstat(2) and readlink(2),
* so the following apparently overflow-proof code may still fail from a buffer
* overflow in the second call to read_symlink():
*
* char *readlink_malloc(const char *path) {
* ssize_t len = read_symlink(path, NULL, 0);
* if (len == -1)
* return NULL;
* char *buf = malloc(len);
* if (buf == NULL)
* return NULL;
* if (read_symlink(path, buf, len) == -1) {
* free(buf);
* return NULL;
* }
* return buf;
* }
*
* @author Andrew Bettison <andrew@servalproject.com>
*/
ssize_t read_symlink(const char *path, char *buf, size_t len);
#endif //__SERVALDNA_OS_H