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coredump,analyze: use read_full_file() for reading various top-level /proc/ files

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Kernel API file systems typically use either "raw" or "seq_file" to
implement their various interface files. The former are really simple
(to point I'd call them broken), in that they have no understanding of
file offsets, and return their contents again and again on every read(),
and thus EOF is indicated by a short read, not by a zero read. The
latter otoh works like a typical file: you read until you get a
zero-sized read back.

We have read_virtual_file() to read the "raw" files, and can use regular
read_full_file() to read the "seq_file" ones.

Apparently all files in the top-level /proc/ directory use 'seq_file'.
but we accidentally used read_virtual_file() for them. Fix that.

Also clarify in a comment what the rules are.

Fixes: #36131
This commit is contained in:
Lennart Poettering 2025-03-13 09:30:23 +01:00
parent cca655dcbf
commit da65941c3e
4 changed files with 14 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/analyze/analyze-filesystems.c
View File

@ -17,7 +17,7 @@ static int load_available_kernel_filesystems(Set **ret) {
/* Let's read the available filesystems */
r = read_virtual_file("/proc/filesystems", SIZE_MAX, &t, NULL);
r = read_full_file("/proc/filesystems", &t, /* ret_size= */ NULL);
if (r < 0)
return r;

6
src/basic/fileio.c
View File

@ -491,7 +491,11 @@ int read_virtual_file_at(
* max_size specifies a limit on the bytes read. If max_size is SIZE_MAX, the full file is read. If
* the full file is too large to read, an error is returned. For other values of max_size, *partial
* contents* may be returned. (Though the read is still done using one syscall.) Returns 0 on
* partial success, 1 if untruncated contents were read. */
* partial success, 1 if untruncated contents were read.
*
* Rule: for kernfs files using "seq_file" → use regular read_full_file_at()
* for kernfs files using "raw" → use read_virtual_file_at()
*/
assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
assert(max_size <= READ_VIRTUAL_BYTES_MAX || max_size == SIZE_MAX);

2
src/basic/proc-cmdline.c
View File

@ -122,7 +122,7 @@ int proc_cmdline(char **ret) {
if (detect_container() > 0)
return pid_get_cmdline(1, SIZE_MAX, 0, ret);
return read_virtual_file("/proc/cmdline", SIZE_MAX, ret, NULL);
return read_full_file("/proc/cmdline", ret, /* ret_size= */ NULL);
}
static int proc_cmdline_strv_internal(char ***ret, bool filter_pid1_args) {

14
src/coredump/coredump.c
View File

@ -1399,28 +1399,28 @@ static int gather_pid_metadata_from_procfs(struct iovec_wrapper *iovw, Context *
(void) iovw_put_string_field_free(iovw, "COREDUMP_OPEN_FDS=", t);
p = procfs_file_alloca(pid, "status");
if (read_full_virtual_file(p, &t, NULL) >= 0)
if (read_full_file(p, &t, /* ret_size= */ NULL) >= 0)
(void) iovw_put_string_field_free(iovw, "COREDUMP_PROC_STATUS=", t);
p = procfs_file_alloca(pid, "maps");
if (read_full_virtual_file(p, &t, NULL) >= 0)
if (read_full_file(p, &t, /* ret_size= */ NULL) >= 0)
(void) iovw_put_string_field_free(iovw, "COREDUMP_PROC_MAPS=", t);
p = procfs_file_alloca(pid, "limits");
if (read_full_virtual_file(p, &t, NULL) >= 0)
p = procfs_file_alloca(pid, "limits"); /* this uses 'seq_file' in kernel, use read_full_file_at() */
if (read_full_file(p, &t, /* ret_size= */ NULL) >= 0)
(void) iovw_put_string_field_free(iovw, "COREDUMP_PROC_LIMITS=", t);
p = procfs_file_alloca(pid, "cgroup");
if (read_full_virtual_file(p, &t, NULL) >= 0)
if (read_full_file(p, &t, /* ret_size= */ NULL) >= 0)
(void) iovw_put_string_field_free(iovw, "COREDUMP_PROC_CGROUP=", t);
p = procfs_file_alloca(pid, "mountinfo");
if (read_full_virtual_file(p, &t, NULL) >= 0)
if (read_full_file(p, &t, /* ret_size= */ NULL) >= 0)
(void) iovw_put_string_field_free(iovw, "COREDUMP_PROC_MOUNTINFO=", t);
/* We attach /proc/auxv here. ELF coredumps also contain a note for this (NT_AUXV), see elf(5). */
p = procfs_file_alloca(pid, "auxv");
if (read_full_virtual_file(p, &t, &size) >= 0) {
if (read_full_file(p, &t, &size) >= 0) {
char *buf = malloc(strlen("COREDUMP_PROC_AUXV=") + size + 1);
if (buf) {
/* Add a dummy terminator to make context_parse_iovw() happy. */