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Merge pull request #7395 from poettering/nametohandleat-loop

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name_to_handle_at() EOVERFLOW handling
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2017-11-22 08:20:36 +01:00
committed by GitHub
parent 5f04a209ea 190654f44b
commit a217a4bcc5
5 changed files with 187 additions and 59 deletions
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src/basic/mount-util.c
+107 -36
View File
@@ -40,6 +40,76 @@
#include "string-util.h"
#include "strv.h"
int name_to_handle_at_loop(
int fd,
const char *path,
struct file_handle **ret_handle,
int *ret_mnt_id,
int flags) {
_cleanup_free_ struct file_handle *h;
size_t n = MAX_HANDLE_SZ;
/* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified
* buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a
* start value, it is not an upper bound on the buffer size required.
*
* This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed
* as NULL if there's no interest in either. */
h = malloc0(offsetof(struct file_handle, f_handle) + n);
if (!h)
return -ENOMEM;
h->handle_bytes = n;
for (;;) {
int mnt_id = -1;
size_t m;
if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
if (ret_handle) {
*ret_handle = h;
h = NULL;
}
if (ret_mnt_id)
*ret_mnt_id = mnt_id;
return 0;
}
if (errno != EOVERFLOW)
return -errno;
if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
/* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW, but
* that's undocumented. Hence, let's make use of this if it appears to be filled in, and the
* caller was interested in only the mount ID an nothing else. */
*ret_mnt_id = mnt_id;
return 0;
}
/* The buffer was too small. Size the new buffer by what name_to_handle_at() returned, but make sure it
* is always larger than what we passed in before */
m = h->handle_bytes > n ? h->handle_bytes : n * 2;
if (m < n) /* Check for multiplication overflow */
return -EOVERFLOW;
if (offsetof(struct file_handle, f_handle) + m < m) /* check for addition overflow */
return -EOVERFLOW;
n = m;
free(h);
h = malloc0(offsetof(struct file_handle, f_handle) + n);
if (!h)
return -ENOMEM;
h->handle_bytes = n;
}
}
static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) {
char path[strlen("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
_cleanup_free_ char *fdinfo = NULL;
@@ -79,7 +149,7 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id
}
int fd_is_mount_point(int fd, const char *filename, int flags) {
union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
_cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL;
int mount_id = -1, mount_id_parent = -1;
bool nosupp = false, check_st_dev = true;
struct stat a, b;
@@ -111,39 +181,30 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
* subvolumes have different st_dev, even though they aren't
* real mounts of their own. */
r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags);
if (r < 0) {
if (IN_SET(errno, ENOSYS, EACCES, EPERM))
/* This kernel does not support name_to_handle_at() at all, or the syscall was blocked (maybe
* through seccomp, because we are running inside of a container?): fall back to simpler
* logic. */
goto fallback_fdinfo;
else if (errno == EOPNOTSUPP)
/* This kernel or file system does not support
* name_to_handle_at(), hence let's see if the
* upper fs supports it (in which case it is a
* mount point), otherwise fallback to the
* traditional stat() logic */
nosupp = true;
else
return -errno;
}
r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
if (IN_SET(r, -ENOSYS, -EACCES, -EPERM))
/* This kernel does not support name_to_handle_at() at all, or the syscall was blocked (maybe through
* seccomp, because we are running inside of a container?): fall back to simpler logic. */
goto fallback_fdinfo;
else if (r == -EOPNOTSUPP)
/* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs
* supports it (in which case it is a mount point), otherwise fallback to the traditional stat()
* logic */
nosupp = true;
else if (r < 0)
return r;
r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH);
if (r < 0) {
if (errno == EOPNOTSUPP) {
if (nosupp)
/* Neither parent nor child do name_to_handle_at()?
We have no choice but to fall back. */
goto fallback_fdinfo;
else
/* The parent can't do name_to_handle_at() but the
* directory we are interested in can?
* If so, it must be a mount point. */
return 1;
} else
return -errno;
}
r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH);
if (r == -EOPNOTSUPP) {
if (nosupp)
/* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */
goto fallback_fdinfo;
else
/* The parent can't do name_to_handle_at() but the directory we are interested in can? If so,
* it must be a mount point. */
return 1;
} else if (r < 0)
return r;
/* The parent can do name_to_handle_at() but the
* directory we are interested in can't? If so, it
@@ -156,9 +217,9 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
* assume this is the root directory, which is a mount
* point. */
if (h.handle.handle_bytes == h_parent.handle.handle_bytes &&
h.handle.handle_type == h_parent.handle.handle_type &&
memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0)
if (h->handle_bytes == h_parent->handle_bytes &&
h->handle_type == h_parent->handle_type &&
memcmp(h->f_handle, h_parent->f_handle, h->handle_bytes) == 0)
return 1;
return mount_id != mount_id_parent;
@@ -241,6 +302,16 @@ int path_is_mount_point(const char *t, const char *root, int flags) {
return fd_is_mount_point(fd, basename(t), flags);
}
int path_get_mnt_id(const char *path, int *ret) {
int r;
r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0);
if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM)) /* kernel/fs don't support this, or seccomp blocks access */
return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret);
return r;
}
int umount_recursive(const char *prefix, int flags) {
bool again;
int n = 0, r;
src/basic/mount-util.h
+4 -7
View File
@@ -30,6 +30,10 @@
#include "macro.h"
#include "missing.h"
int name_to_handle_at_loop(int fd, const char *path, struct file_handle **ret_handle, int *ret_mnt_id, int flags);
int path_get_mnt_id(const char *path, int *ret);
int fd_is_mount_point(int fd, const char *filename, int flags);
int path_is_mount_point(const char *path, const char *root, int flags);
@@ -49,15 +53,8 @@ bool fstype_is_api_vfs(const char *fstype);
bool fstype_is_ro(const char *fsype);
bool fstype_can_discard(const char *fstype);
union file_handle_union {
struct file_handle handle;
char padding[sizeof(struct file_handle) + MAX_HANDLE_SZ];
};
const char* mode_to_inaccessible_node(mode_t mode);
#define FILE_HANDLE_INIT { .handle.handle_bytes = MAX_HANDLE_SZ }
int mount_verbose(
int error_log_level,
const char *what,