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binutils: Avoid renaming over existing files

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Renaming over existing files needs additional care to restore
permissions and ownership, which may not always succeed.
Additionally, other properties of the file such as extended attributes
may be lost, making the operation flaky.

For predictable results, resort to rename() only if the file does not
exist, otherwise copy the file contents into the existing file.  This
ensures that no additional tricks are needed to retain file
properties.

This also allows dropping of the redundant set_times on the tmpfile in
objcopy/strip since now we no longer rename over existing files.

binutils/

	* ar.c (write_archive): Remove TARGET_STAT.  Adjust call to
	SMART_RENAME.
	* arsup.c (ar_save): Likewise.
	* objcopy (strip_main): Don't copy TMPFD.  Don't set times on
	temporary file and adjust call to SMART_RENAME.
	(copy_main): Likewise.
	* rename.c [!S_ISLNK]: Remove definitions.
	(try_preserve_permissions): Remove function.
	(smart_rename): Remove FD, PRESERVE_DATES arguments.  Use
	rename system call only if TO does not exist.
	* bucomm.h (smart_rename): Adjust declaration.
This commit is contained in:
Siddhesh Poyarekar
2021-02-19 08:05:33 +05:30
parent 668c18f17f
commit 3685de750e
6 changed files with 33 additions and 142 deletions
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95
binutils/rename.c
View File

@ -122,61 +122,13 @@ set_times (const char *destination, const struct stat *statbuf)
non_fatal (_("%s: cannot set time: %s"), destination, strerror (errno));
}
#ifndef S_ISLNK
#ifdef S_IFLNK
#define S_ISLNK(m) (((m) & S_IFMT) == S_IFLNK)
#else
#define S_ISLNK(m) 0
#define lstat stat
#endif
#endif
#if !defined (_WIN32) || defined (__CYGWIN32__)
/* Try to preserve the permission bits and ownership of an existing file when
rename overwrites it. FD is the file being renamed and TARGET_STAT has the
status of the file that was overwritten. */
static void
try_preserve_permissions (int fd, struct stat *target_stat)
{
struct stat from_stat;
int ret = 0;
if (fstat (fd, &from_stat) != 0)
return;
int from_mode = from_stat.st_mode & 0777;
int to_mode = target_stat->st_mode & 0777;
/* Fix up permissions before we potentially lose ownership with fchown.
Clear the setxid bits because in case the fchown below fails then we don't
want to end up with a sxid file owned by the invoking user. If the user
hasn't changed or if fchown succeeded, we add back the sxid bits at the
end. */
if (from_mode != to_mode)
fchmod (fd, to_mode);
/* Fix up ownership, this will clear the setxid bits. */
if (from_stat.st_uid != target_stat->st_uid
|| from_stat.st_gid != target_stat->st_gid)
ret = fchown (fd, target_stat->st_uid, target_stat->st_gid);
/* Fix up the sxid bits if either the fchown wasn't needed or it
succeeded. */
if (ret == 0)
fchmod (fd, target_stat->st_mode & 07777);
}
#endif
/* Rename FROM to TO, copying if TO is either a link or is not a regular file.
FD is an open file descriptor pointing to FROM that we can use to safely fix
up permissions of the file after renaming. TARGET_STAT has the file status
that is used to fix up permissions and timestamps after rename. Return 0 if
ok, -1 if error and FD is closed before returning. */
/* Rename FROM to TO, copying if TO exists. TARGET_STAT has the file status
that, if non-NULL, is used to fix up timestamps after rename. Return 0 if
ok, -1 if error. */
int
smart_rename (const char *from, const char *to, int fd ATTRIBUTE_UNUSED,
struct stat *target_stat ATTRIBUTE_UNUSED,
int preserve_dates ATTRIBUTE_UNUSED)
smart_rename (const char *from, const char *to,
struct stat *target_stat ATTRIBUTE_UNUSED)
{
int ret = 0;
struct stat to_stat;
@ -199,37 +151,10 @@ smart_rename (const char *from, const char *to, int fd ATTRIBUTE_UNUSED,
unlink (from);
}
#else
/* Avoid a full copy and use rename if we can fix up permissions of the
file after renaming, i.e.:
- TO is not a symbolic link
- TO is a regular file with only one hard link
- We have permission to write to TO
- FD is available to safely fix up permissions to be the same as the file
we overwrote with the rename.
Note though that the actual file on disk that TARGET_STAT describes may
have changed and we're only trying to preserve the status we know about.
At no point do we try to interact with the new file changes, so there can
only be two outcomes, i.e. either the external file change survives
without knowledge of our change (if it happens after the rename syscall)
or our rename and permissions fixup survive without any knowledge of the
external change. */
if (! exists
|| (fd >= 0
&& !S_ISLNK (to_stat.st_mode)
&& S_ISREG (to_stat.st_mode)
&& (to_stat.st_mode & S_IWUSR)
&& to_stat.st_nlink == 1)
)
/* Avoid a full copy and use rename if TO does not exist. */
if (!exists)
{
ret = rename (from, to);
if (ret == 0)
{
if (exists && target_stat != NULL)
try_preserve_permissions (fd, target_stat);
}
else
if ((ret = rename (from, to)) != 0)
{
/* We have to clean up here. */
non_fatal (_("unable to rename '%s'; reason: %s"), to, strerror (errno));
@ -242,12 +167,10 @@ smart_rename (const char *from, const char *to, int fd ATTRIBUTE_UNUSED,
if (ret != 0)
non_fatal (_("unable to copy file '%s'; reason: %s"), to, strerror (errno));
if (preserve_dates && target_stat != NULL)
if (target_stat != NULL)
set_times (to, target_stat);
unlink (from);
}
if (fd >= 0)
close (fd);
#endif /* _WIN32 && !__CYGWIN32__ */
return ret;