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rootless: add fallback for renameat2 at runtime 

the renameat2 syscall might be defined in the C library but lacking
support in the kernel.

In such case, let it fallback to open(O_CREAT)+rename as it does on
systems lacking the definition for renameat2.

Closes: https://github.com/containers/libpod/issues/4570

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
This commit is contained in:
Giuseppe Scrivano 2019-12-04 10:25:54 +01:00
parent 5c3af009c6
commit a94e625868
No known key found for this signature in database
GPG Key ID: E4730F97F60286ED
1 changed files with 20 additions and 13 deletions
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33
pkg/rootless/rootless_linux.c
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@ -19,24 +19,31 @@
#include <sys/select.h>
#include <stdio.h>
#ifndef RENAME_NOREPLACE
# define RENAME_NOREPLACE (1 << 0)
int renameat2 (int olddirfd, const char *oldpath, int newdirfd, const char *newpath, unsigned int flags)
int rename_noreplace (int olddirfd, const char *oldpath, int newdirfd, const char *newpath)
{
int ret;
# ifdef SYS_renameat2
return (int) syscall (SYS_renameat2, olddirfd, oldpath, newdirfd, newpath, flags);
# else
# ifndef RENAME_NOREPLACE
# define RENAME_NOREPLACE (1 << 0)
# endif
ret = (int) syscall (SYS_renameat2, olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE);
if (ret == 0 || errno != EINVAL)
return ret;
/* Fallback in case of errno==EINVAL. */
# endif
/* This might be an issue if another process is trying to read the file while it is empty. */
int fd = open (newpath, O_EXCL|O_CREAT, 0700);
if (fd < 0)
return fd;
close (fd);
ret = open (newpath, O_EXCL|O_CREAT, 0700);
if (ret < 0)
return ret;
close (ret);
/* We are sure we created the file, let's overwrite it. */
return rename (oldpath, newpath);
# endif
}
#endif
#ifndef TEMP_FAILURE_RETRY
#define TEMP_FAILURE_RETRY(expression) \
@ -453,7 +460,7 @@ create_pause_process (const char *pause_pid_file_path, char **argv)
/* There can be another process at this point trying to configure the user namespace and the pause
process, do not override the pid file if it already exists. */
if (renameat2 (AT_FDCWD, tmp_file_path, AT_FDCWD, pause_pid_file_path, RENAME_NOREPLACE) < 0)
if (rename_noreplace (AT_FDCWD, tmp_file_path, AT_FDCWD, pause_pid_file_path) < 0)
{
unlink (tmp_file_path);
kill (pid, SIGKILL);