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core: when we cannot open an image file for write, try read-only

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Closes: #14442
This commit is contained in:
Lennart Poettering 2020-01-07 16:56:05 +01:00
parent c8c535d589
commit b0a94268f8
2 changed files with 22 additions and 5 deletions
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2
src/core/namespace.c
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@ -1289,7 +1289,7 @@ int setup_namespace(
dissect_image_flags |= DISSECT_IMAGE_READ_ONLY;
r = loop_device_make_by_path(root_image,
dissect_image_flags & DISSECT_IMAGE_READ_ONLY ? O_RDONLY : O_RDWR,
FLAGS_SET(dissect_image_flags, DISSECT_IMAGE_READ_ONLY) ? O_RDONLY : -1 /* < 0 means writable if possible, read-only as fallback */,
LO_FLAGS_PARTSCAN,
&loop_device);
if (r < 0)

25
src/shared/loop-util.c
View File

@ -14,6 +14,7 @@
#include <unistd.h>
#include "alloc-util.h"
#include "errno-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "loop-util.h"
@ -157,14 +158,30 @@ int loop_device_make(
int loop_device_make_by_path(const char *path, int open_flags, uint32_t loop_flags, LoopDevice **ret) {
_cleanup_close_ int fd = -1;
int r;
assert(path);
assert(ret);
assert(IN_SET(open_flags, O_RDWR, O_RDONLY));
assert(open_flags < 0 || IN_SET(open_flags, O_RDWR, O_RDONLY));
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (fd < 0)
return -errno;
/* Passing < 0 as open_flags here means we'll try to open the device writable if we can, retrying
* read-only if we cannot. */
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|(open_flags >= 0 ? open_flags : O_RDWR));
if (fd < 0) {
r = -errno;
/* Retry read-only? */
if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS))
return r;
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|O_RDONLY);
if (fd < 0)
return r; /* Propagate original error */
open_flags = O_RDONLY;
} else if (open_flags < 0)
open_flags = O_RDWR;
return loop_device_make(fd, open_flags, 0, 0, loop_flags, ret);
}