[PATCH v3 2/3] depmod: prevent module dependency files corruption due to parallel invocation.
From: Michal Suchanek <hidden>
Date: 2018-12-17 22:46:50
Subsystem:
the rest · Maintainer:
Linus Torvalds
Depmod does not use unique filename for temporary files. There is no guarantee the user does not attempt to run mutiple depmod processes in parallel. If that happens a temporary file might be created by depmod(1st), truncated by depmod(2nd), and renamed to final name by depmod(1st) resulting in corrupted file seen by user. Due to missing mkstempat() this is more complex than it should be. Adding PID and timestamp to the filename should be reasonably reliable. Adding O_EXCL as mkstemp does fails creating the file rather than corrupting existing file. Signed-off-by: Michal Suchanek <redacted> --- v3: - remove superfluous code to terminate the string - snprintf should do it - remove superfluous O_TRUNC - not needed with O_EXCL --- tools/depmod.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/tools/depmod.c b/tools/depmod.c
index 18c0d61b2db3..0f7e33ccfd59 100644
--- a/tools/depmod.c
+++ b/tools/depmod.c@@ -29,6 +29,7 @@ #include <string.h> #include <unistd.h> #include <sys/stat.h> +#include <sys/time.h> #include <sys/utsname.h> #include <shared/array.h>
@@ -2398,6 +2399,9 @@ static int depmod_output(struct depmod *depmod, FILE *out) }; const char *dname = depmod->cfg->dirname; int dfd, err = 0; + struct timeval tv; + + gettimeofday(&tv, NULL); if (out != NULL) dfd = -1;
@@ -2416,11 +2420,12 @@ static int depmod_output(struct depmod *depmod, FILE *out) int r, ferr; if (fp == NULL) { - int flags = O_CREAT | O_TRUNC | O_WRONLY; + int flags = O_CREAT | O_EXCL | O_WRONLY; int mode = 0644; int fd; - snprintf(tmp, sizeof(tmp), "%s.tmp", itr->name); + snprintf(tmp, sizeof(tmp), "%s.%i.%li.%li", itr->name, getpid(), + tv.tv_usec, tv.tv_sec); fd = openat(dfd, tmp, flags, mode); if (fd < 0) { ERR("openat(%s, %s, %o, %o): %m\n",
--
2.19.2