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patch 8.0.1300: file permissions may end up wrong when writing

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Problem:    File permissions may end up wrong when writing.
Solution:   Use fchmod() instead of chmod() when possible.  Don't truncate
            until we know we can change the file.
This commit is contained in:
Bram Moolenaar
2017-11-16 17:03:45 +01:00
parent a42ad57e48
commit cd142e3369
7 changed files with 88 additions and 24 deletions
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80
src/fileio.c
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@@ -3863,6 +3863,7 @@ buf_write(
char_u *rootname;
#if defined(UNIX)
int did_set_shortname;
mode_t umask_save;
#endif
copybuf = alloc(BUFSIZE + 1);
@@ -3994,10 +3995,17 @@ buf_write(
/* remove old backup, if present */
mch_remove(backup);
/* Open with O_EXCL to avoid the file being created while
* we were sleeping (symlink hacker attack?) */
* we were sleeping (symlink hacker attack?). Reset umask
* if possible to avoid mch_setperm() below. */
#ifdef UNIX
umask_save = umask(0);
#endif
bfd = mch_open((char *)backup,
O_WRONLY|O_CREAT|O_EXTRA|O_EXCL|O_NOFOLLOW,
perm & 0777);
#ifdef UNIX
(void)umask(umask_save);
#endif
if (bfd < 0)
{
vim_free(backup);
@@ -4005,11 +4013,12 @@ buf_write(
}
else
{
/* set file protection same as original file, but
* strip s-bit */
/* Set file protection same as original file, but
* strip s-bit. Only needed if umask() wasn't used
* above. */
#ifndef UNIX
(void)mch_setperm(backup, perm & 0777);
#ifdef UNIX
#else
/*
* Try to set the group of the backup same as the
* original file. If this fails, set the protection
@@ -4377,6 +4386,11 @@ buf_write(
}
else
{
#ifdef HAVE_FTRUNCATE
# define TRUNC_ON_OPEN 0
#else
# define TRUNC_ON_OPEN O_TRUNC
#endif
/*
* Open the file "wfname" for writing.
* We may try to open the file twice: If we can't write to the file
@@ -4389,7 +4403,7 @@ buf_write(
*/
while ((fd = mch_open((char *)wfname, O_WRONLY | O_EXTRA | (append
? (forceit ? (O_APPEND | O_CREAT) : O_APPEND)
: (O_CREAT | O_TRUNC))
: (O_CREAT | TRUNC_ON_OPEN))
, perm < 0 ? 0666 : (perm & 0777))) < 0)
{
/*
@@ -4482,6 +4496,30 @@ restore_backup:
}
write_info.bw_fd = fd;
#if defined(UNIX)
{
stat_T st;
/* Double check we are writing the intended file before making
* any changes. */
if (overwriting
&& (!dobackup || backup_copy)
&& fname == wfname
&& perm >= 0
&& mch_fstat(fd, &st) == 0
&& st.st_ino != st_old.st_ino)
{
close(fd);
errmsg = (char_u *)_("E949: File changed while writing");
goto fail;
}
}
#endif
#ifdef HAVE_FTRUNCATE
if (!append)
ftruncate(fd, (off_t)0);
#endif
#if defined(WIN3264)
if (backup != NULL && overwriting && !append)
{
@@ -4752,15 +4790,17 @@ restore_backup:
# ifdef HAVE_FCHOWN
stat_T st;
/* don't change the owner when it's already OK, some systems remove
* permission or ACL stuff */
/* Don't change the owner when it's already OK, some systems remove
* permission or ACL stuff. */
if (mch_stat((char *)wfname, &st) < 0
|| st.st_uid != st_old.st_uid
|| st.st_gid != st_old.st_gid)
{
ignored = fchown(fd, st_old.st_uid, st_old.st_gid);
if (perm >= 0) /* set permission again, may have changed */
(void)mch_setperm(wfname, perm);
/* changing owner might not be possible */
ignored = fchown(fd, st_old.st_uid, -1);
/* if changing group fails clear the group permissions */
if (fchown(fd, -1, st_old.st_gid) == -1 && perm > 0)
perm &= ~070;
}
# endif
buf_setino(buf);
@@ -4770,18 +4810,26 @@ restore_backup:
buf_setino(buf);
#endif
#ifdef UNIX
if (made_writable)
perm &= ~0200; /* reset 'w' bit for security reasons */
#endif
#ifdef HAVE_FCHMOD
/* set permission of new file same as old file */
if (perm >= 0)
(void)mch_fsetperm(fd, perm);
#endif
if (close(fd) != 0)
{
errmsg = (char_u *)_("E512: Close failed");
end = 0;
}
#ifdef UNIX
if (made_writable)
perm &= ~0200; /* reset 'w' bit for security reasons */
#endif
if (perm >= 0) /* set perm. of new file same as old file */
#ifndef HAVE_FCHMOD
/* set permission of new file same as old file */
if (perm >= 0)
(void)mch_setperm(wfname, perm);
#endif
#ifdef HAVE_ACL
/*
* Probably need to set the ACL before changing the user (can't set the