diff options
Diffstat (limited to 'src/basic')
| -rw-r--r-- | src/basic/fileio.c | 115 | ||||
| -rw-r--r-- | src/basic/fileio.h | 1 |
2 files changed, 112 insertions, 4 deletions
diff --git a/src/basic/fileio.c b/src/basic/fileio.c index a9c0fd20e1..e1600a1e6a 100644 --- a/src/basic/fileio.c +++ b/src/basic/fileio.c @@ -310,6 +310,113 @@ int verify_file(const char *fn, const char *blob, bool accept_extra_nl) { return 1; } +int read_full_virtual_file(const char *filename, char **ret_contents, size_t *ret_size) { + _cleanup_free_ char *buf = NULL; + _cleanup_close_ int fd = -1; + struct stat st; + size_t n, size; + int n_retries; + char *p; + + assert(ret_contents); + + /* Virtual filesystems such as sysfs or procfs use kernfs, and kernfs can work + * with two sorts of virtual files. One sort uses "seq_file", and the results of + * the first read are buffered for the second read. The other sort uses "raw" + * reads which always go direct to the device. In the latter case, the content of + * the virtual file must be retrieved with a single read otherwise a second read + * might get the new value instead of finding EOF immediately. That's the reason + * why the usage of fread(3) is prohibited in this case as it always performs a + * second call to read(2) looking for EOF. See issue 13585. */ + + fd = open(filename, O_RDONLY|O_CLOEXEC); + if (fd < 0) + return -errno; + + /* Start size for files in /proc which usually report a file size of 0. */ + size = LINE_MAX / 2; + + /* Limit the number of attempts to read the number of bytes returned by fstat(). */ + n_retries = 3; + + for (;;) { + if (n_retries <= 0) + return -EIO; + + if (fstat(fd, &st) < 0) + return -errno; + + if (!S_ISREG(st.st_mode)) + return -EBADF; + + /* Be prepared for files from /proc which generally report a file size of 0. */ + if (st.st_size > 0) { + size = st.st_size; + n_retries--; + } else + size = size * 2; + + if (size > READ_FULL_BYTES_MAX) + return -E2BIG; + + p = realloc(buf, size + 1); + if (!p) + return -ENOMEM; + buf = TAKE_PTR(p); + + for (;;) { + ssize_t k; + + /* Read one more byte so we can detect whether the content of the + * file has already changed or the guessed size for files from /proc + * wasn't large enough . */ + k = read(fd, buf, size + 1); + if (k >= 0) { + n = k; + break; + } + + if (errno != -EINTR) + return -errno; + } + + /* Consider a short read as EOF */ + if (n <= size) + break; + + /* Hmm... either we read too few bytes from /proc or less likely the content + * of the file might have been changed (and is now bigger) while we were + * processing, let's try again either with a bigger guessed size or the new + * file size. */ + + if (lseek(fd, 0, SEEK_SET) < 0) + return -errno; + } + + if (n < size) { + p = realloc(buf, n + 1); + if (!p) + return -ENOMEM; + buf = TAKE_PTR(p); + } + + if (!ret_size) { + /* Safety check: if the caller doesn't want to know the size of what we + * just read it will rely on the trailing NUL byte. But if there's an + * embedded NUL byte, then we should refuse operation as otherwise + * there'd be ambiguity about what we just read. */ + + if (memchr(buf, 0, n)) + return -EBADMSG; + } else + *ret_size = n; + + buf[n] = 0; + *ret_contents = TAKE_PTR(buf); + + return 0; +} + int read_full_stream_full( FILE *f, const char *filename, @@ -342,9 +449,9 @@ int read_full_stream_full( if (st.st_size > READ_FULL_BYTES_MAX) return -E2BIG; - /* Start with the right file size, but be prepared for files from /proc which generally report a file - * size of 0. Note that we increase the size to read here by one, so that the first read attempt - * already makes us notice the EOF. */ + /* Start with the right file size. Note that we increase the size + * to read here by one, so that the first read attempt already + * makes us notice the EOF. */ if (st.st_size > 0) n_next = st.st_size + 1; @@ -502,7 +609,7 @@ int get_proc_field(const char *filename, const char *pattern, const char *termin assert(pattern); assert(field); - r = read_full_file(filename, &status, NULL); + r = read_full_virtual_file(filename, &status, NULL); if (r < 0) return r; diff --git a/src/basic/fileio.h b/src/basic/fileio.h index 05f6c89da0..31bfef33ac 100644 --- a/src/basic/fileio.h +++ b/src/basic/fileio.h @@ -56,6 +56,7 @@ int read_full_file_full(const char *filename, ReadFullFileFlags flags, char **co static inline int read_full_file(const char *filename, char **contents, size_t *size) { return read_full_file_full(filename, 0, contents, size); } +int read_full_virtual_file(const char *filename, char **ret_contents, size_t *ret_size); int read_full_stream_full(FILE *f, const char *filename, ReadFullFileFlags flags, char **contents, size_t *size); static inline int read_full_stream(FILE *f, char **contents, size_t *size) { return read_full_stream_full(f, NULL, 0, contents, size); |