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export/fuse: Let permissions be adjustable

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Allow changing the file mode, UID, and GID through SETATTR.

Without allow_other, UID and GID are not allowed to be changed, because
it would not make sense.  Also, changing group or others' permissions
is not allowed either.

For read-only exports, +w cannot be set.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210625142317.271673-5-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2021-06-25 16:23:15 +02:00 committed by Kevin Wolf
parent 9bad96a8cc
commit 6aeeaed29c
1 changed files with 62 additions and 11 deletions
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73
block/export/fuse.c
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@ -48,6 +48,10 @@ typedef struct FuseExport {
bool growable;
/* Whether allow_other was used as a mount option or not */
bool allow_other;
mode_t st_mode;
uid_t st_uid;
gid_t st_gid;
} FuseExport;
static GHashTable *exports;
@ -125,6 +129,13 @@ static int fuse_export_create(BlockExport *blk_exp,
args->allow_other = FUSE_EXPORT_ALLOW_OTHER_AUTO;
}
exp->st_mode = S_IFREG | S_IRUSR;
if (exp->writable) {
exp->st_mode |= S_IWUSR;
}
exp->st_uid = getuid();
exp->st_gid = getgid();
if (args->allow_other == FUSE_EXPORT_ALLOW_OTHER_AUTO) {
/* Ignore errors on our first attempt */
ret = setup_fuse_export(exp, args->mountpoint, true, NULL);
@ -338,7 +349,6 @@ static void fuse_getattr(fuse_req_t req, fuse_ino_t inode,
int64_t length, allocated_blocks;
time_t now = time(NULL);
FuseExport *exp = fuse_req_userdata(req);
mode_t mode;
length = blk_getlength(exp->common.blk);
if (length < 0) {
@ -353,17 +363,12 @@ static void fuse_getattr(fuse_req_t req, fuse_ino_t inode,
allocated_blocks = DIV_ROUND_UP(allocated_blocks, 512);
}
mode = S_IFREG | S_IRUSR;
if (exp->writable) {
mode |= S_IWUSR;
}
statbuf = (struct stat) {
.st_ino = inode,
.st_mode = mode,
.st_mode = exp->st_mode,
.st_nlink = 1,
.st_uid = getuid(),
.st_gid = getgid(),
.st_uid = exp->st_uid,
.st_gid = exp->st_gid,
.st_size = length,
.st_blksize = blk_bs(exp->common.blk)->bl.request_alignment,
.st_blocks = allocated_blocks,
@ -409,19 +414,52 @@ static int fuse_do_truncate(const FuseExport *exp, int64_t size,
}
/**
* Let clients set file attributes. Only resizing is supported.
* Let clients set file attributes. Only resizing and changing
* permissions (st_mode, st_uid, st_gid) is allowed.
* Changing permissions is only allowed as far as it will actually
* permit access: Read-only exports cannot be given +w, and exports
* without allow_other cannot be given a different UID or GID, and
* they cannot be given non-owner access.
*/
static void fuse_setattr(fuse_req_t req, fuse_ino_t inode, struct stat *statbuf,
int to_set, struct fuse_file_info *fi)
{
FuseExport *exp = fuse_req_userdata(req);
int supported_attrs;
int ret;
if (to_set & ~FUSE_SET_ATTR_SIZE) {
supported_attrs = FUSE_SET_ATTR_SIZE | FUSE_SET_ATTR_MODE;
if (exp->allow_other) {
supported_attrs |= FUSE_SET_ATTR_UID | FUSE_SET_ATTR_GID;
}
if (to_set & ~supported_attrs) {
fuse_reply_err(req, ENOTSUP);
return;
}
/* Do some argument checks first before committing to anything */
if (to_set & FUSE_SET_ATTR_MODE) {
/*
* Without allow_other, non-owners can never access the export, so do
* not allow setting permissions for them
*/
if (!exp->allow_other &&
(statbuf->st_mode & (S_IRWXG | S_IRWXO)) != 0)
{
fuse_reply_err(req, EPERM);
return;
}
/* +w for read-only exports makes no sense, disallow it */
if (!exp->writable &&
(statbuf->st_mode & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
{
fuse_reply_err(req, EROFS);
return;
}
}
if (to_set & FUSE_SET_ATTR_SIZE) {
if (!exp->writable) {
fuse_reply_err(req, EACCES);
@ -435,6 +473,19 @@ static void fuse_setattr(fuse_req_t req, fuse_ino_t inode, struct stat *statbuf,
}
}
if (to_set & FUSE_SET_ATTR_MODE) {
/* Ignore FUSE-supplied file type, only change the mode */
exp->st_mode = (statbuf->st_mode & 07777) | S_IFREG;
}
if (to_set & FUSE_SET_ATTR_UID) {
exp->st_uid = statbuf->st_uid;
}
if (to_set & FUSE_SET_ATTR_GID) {
exp->st_gid = statbuf->st_gid;
}
fuse_getattr(req, inode, fi);
}