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fuse: check attributes staleness on fuse_iget()

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Function fuse_direntplus_link() might call fuse_iget() to initialize a new
fuse_inode and change its attributes. If fi->attr_version is always
initialized with 0, even if the attributes returned by the FUSE_READDIR
request is staled, as the new fi->attr_version is 0, fuse_change_attributes
will still set the staled attributes to inode. This wrong behaviour may
cause file size inconsistency even when there is no changes from
server-side.

To reproduce the issue, consider the following 2 programs (A and B) are
running concurrently,

        A                                               B
----------------------------------      --------------------------------
{ /fusemnt/dir/f is a file path in a fuse mount, the size of f is 0. }

readdir(/fusemnt/dir) start
//Daemon set size 0 to f direntry
                                        fallocate(f, 1024)
                                        stat(f) // B see size 1024
                                        echo 2 > /proc/sys/vm/drop_caches
readdir(/fusemnt/dir) reply to kernel
Kernel set 0 to the I_NEW inode

                                        stat(f) // B see size 0

In the above case, only program B is modifying the file size, however, B
observes file size changing between the 2 'readonly' stat() calls. To fix
this issue, we should make sure readdirplus still follows the rule of
attr_version staleness checking even if the fi->attr_version is lost due to
inode eviction.

To identify this situation, the new fc->evict_ctr is used to record whether
the eviction of inodes occurs during the readdirplus request processing.
If it does, the result of readdirplus may be inaccurate; otherwise, the
result of readdirplus can be trusted. Although this may still lead to
incorrect invalidation, considering the relatively low frequency of
evict occurrences, it should be acceptable.

Link: https://lore.kernel.org/lkml/20230711043405.66256-2-zhangjiachen.jaycee@bytedance.com/
Link: https://lore.kernel.org/lkml/20241114070905.48901-1-zhangtianci.1997@bytedance.com/

Reported-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Suggested-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Zhang Tianci <zhangtianci.1997@bytedance.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Zhang Tianci 2024-11-18 18:16:00 +08:00 committed by Miklos Szeredi
parent 68bfb7eb7f
commit 69eb56f69e
4 changed files with 71 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/fuse/dir.c
View File

@ -366,7 +366,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
struct fuse_mount *fm = get_fuse_mount_super(sb);
FUSE_ARGS(args);
struct fuse_forget_link *forget;
u64 attr_version;
u64 attr_version, evict_ctr;
int err;
*inode = NULL;
@ -381,6 +381,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
goto out;
attr_version = fuse_get_attr_version(fm->fc);
evict_ctr = fuse_get_evict_ctr(fm->fc);
fuse_lookup_init(fm->fc, &args, nodeid, name, outarg);
err = fuse_simple_request(fm, &args);
@ -398,7 +399,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
*inode = fuse_iget(sb, outarg->nodeid, outarg->generation,
&outarg->attr, ATTR_TIMEOUT(outarg),
attr_version);
attr_version, evict_ctr);
err = -ENOMEM;
if (!*inode) {
fuse_queue_forget(fm->fc, forget, outarg->nodeid, 1);
@ -691,7 +692,7 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
ff->nodeid = outentry.nodeid;
ff->open_flags = outopenp->open_flags;
inode = fuse_iget(dir->i_sb, outentry.nodeid, outentry.generation,
&outentry.attr, ATTR_TIMEOUT(&outentry), 0);
&outentry.attr, ATTR_TIMEOUT(&outentry), 0, 0);
if (!inode) {
flags &= ~(O_CREAT | O_EXCL | O_TRUNC);
fuse_sync_release(NULL, ff, flags);
@ -822,7 +823,7 @@ static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
goto out_put_forget_req;
inode = fuse_iget(dir->i_sb, outarg.nodeid, outarg.generation,
&outarg.attr, ATTR_TIMEOUT(&outarg), 0);
&outarg.attr, ATTR_TIMEOUT(&outarg), 0, 0);
if (!inode) {
fuse_queue_forget(fm->fc, forget, outarg.nodeid, 1);
return -ENOMEM;
@ -2028,7 +2029,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
fuse_change_attributes_common(inode, &outarg.attr, NULL,
ATTR_TIMEOUT(&outarg),
fuse_get_cache_mask(inode));
fuse_get_cache_mask(inode), 0);
oldsize = inode->i_size;
/* see the comment in fuse_change_attributes() */
if (!is_wb || is_truncate)

14
fs/fuse/fuse_i.h
View File

@ -890,6 +890,9 @@ struct fuse_conn {
/** Version counter for attribute changes */
atomic64_t attr_version;
/** Version counter for evict inode */
atomic64_t evict_ctr;
/** Called on final put */
void (*release)(struct fuse_conn *);
@ -984,6 +987,11 @@ static inline u64 fuse_get_attr_version(struct fuse_conn *fc)
return atomic64_read(&fc->attr_version);
}
static inline u64 fuse_get_evict_ctr(struct fuse_conn *fc)
{
return atomic64_read(&fc->evict_ctr);
}
static inline bool fuse_stale_inode(const struct inode *inode, int generation,
struct fuse_attr *attr)
{
@ -1043,7 +1051,8 @@ extern const struct dentry_operations fuse_root_dentry_operations;
*/
struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
int generation, struct fuse_attr *attr,
u64 attr_valid, u64 attr_version);
u64 attr_valid, u64 attr_version,
u64 evict_ctr);
int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name,
struct fuse_entry_out *outarg, struct inode **inode);
@ -1133,7 +1142,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
struct fuse_statx *sx,
u64 attr_valid, u32 cache_mask);
u64 attr_valid, u32 cache_mask,
u64 evict_ctr);
u32 fuse_get_cache_mask(struct inode *inode);

56
fs/fuse/inode.c
View File

@ -175,6 +175,14 @@ static void fuse_evict_inode(struct inode *inode)
fuse_cleanup_submount_lookup(fc, fi->submount_lookup);
fi->submount_lookup = NULL;
}
/*
* Evict of non-deleted inode may race with outstanding
* LOOKUP/READDIRPLUS requests and result in inconsistency when
* the request finishes. Deal with that here by bumping a
* counter that can be compared to the starting value.
*/
if (inode->i_nlink > 0)
atomic64_inc(&fc->evict_ctr);
}
if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
WARN_ON(fi->iocachectr != 0);
@ -208,17 +216,30 @@ static ino_t fuse_squash_ino(u64 ino64)
void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
struct fuse_statx *sx,
u64 attr_valid, u32 cache_mask)
u64 attr_valid, u32 cache_mask,
u64 evict_ctr)
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
lockdep_assert_held(&fi->lock);
/*
* Clear basic stats from invalid mask.
*
* Don't do this if this is coming from a fuse_iget() call and there
* might have been a racing evict which would've invalidated the result
* if the attr_version would've been preserved.
*
* !evict_ctr -> this is create
* fi->attr_version != 0 -> this is not a new inode
* evict_ctr == fuse_get_evict_ctr() -> no evicts while during request
*/
if (!evict_ctr || fi->attr_version || evict_ctr == fuse_get_evict_ctr(fc))
set_mask_bits(&fi->inval_mask, STATX_BASIC_STATS, 0);
fi->attr_version = atomic64_inc_return(&fc->attr_version);
fi->i_time = attr_valid;
/* Clear basic stats from invalid mask */
set_mask_bits(&fi->inval_mask, STATX_BASIC_STATS, 0);
inode->i_ino = fuse_squash_ino(attr->ino);
inode->i_mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
@ -297,9 +318,9 @@ u32 fuse_get_cache_mask(struct inode *inode)
return STATX_MTIME | STATX_CTIME | STATX_SIZE;
}
void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
struct fuse_statx *sx,
u64 attr_valid, u64 attr_version)
static void fuse_change_attributes_i(struct inode *inode, struct fuse_attr *attr,
struct fuse_statx *sx, u64 attr_valid,
u64 attr_version, u64 evict_ctr)
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
@ -333,7 +354,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
}
old_mtime = inode_get_mtime(inode);
fuse_change_attributes_common(inode, attr, sx, attr_valid, cache_mask);
fuse_change_attributes_common(inode, attr, sx, attr_valid, cache_mask,
evict_ctr);
oldsize = inode->i_size;
/*
@ -374,6 +396,13 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
fuse_dax_dontcache(inode, attr->flags);
}
void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
struct fuse_statx *sx, u64 attr_valid,
u64 attr_version)
{
fuse_change_attributes_i(inode, attr, sx, attr_valid, attr_version, 0);
}
static void fuse_init_submount_lookup(struct fuse_submount_lookup *sl,
u64 nodeid)
{
@ -428,7 +457,8 @@ static int fuse_inode_set(struct inode *inode, void *_nodeidp)
struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
int generation, struct fuse_attr *attr,
u64 attr_valid, u64 attr_version)
u64 attr_valid, u64 attr_version,
u64 evict_ctr)
{
struct inode *inode;
struct fuse_inode *fi;
@ -489,8 +519,8 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
fi->nlookup++;
spin_unlock(&fi->lock);
done:
fuse_change_attributes(inode, attr, NULL, attr_valid, attr_version);
fuse_change_attributes_i(inode, attr, NULL, attr_valid, attr_version,
evict_ctr);
return inode;
}
@ -942,6 +972,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
fc->initialized = 0;
fc->connected = 1;
atomic64_set(&fc->attr_version, 1);
atomic64_set(&fc->evict_ctr, 1);
get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
fc->user_ns = get_user_ns(user_ns);
@ -1003,7 +1034,7 @@ static struct inode *fuse_get_root_inode(struct super_block *sb, unsigned mode)
attr.mode = mode;
attr.ino = FUSE_ROOT_ID;
attr.nlink = 1;
return fuse_iget(sb, FUSE_ROOT_ID, 0, &attr, 0, 0);
return fuse_iget(sb, FUSE_ROOT_ID, 0, &attr, 0, 0, 0);
}
struct fuse_inode_handle {
@ -1612,7 +1643,8 @@ static int fuse_fill_super_submount(struct super_block *sb,
return -ENOMEM;
fuse_fill_attr_from_inode(&root_attr, parent_fi);
root = fuse_iget(sb, parent_fi->nodeid, 0, &root_attr, 0, 0);
root = fuse_iget(sb, parent_fi->nodeid, 0, &root_attr, 0, 0,
fuse_get_evict_ctr(fm->fc));
/*
* This inode is just a duplicate, so it is not looked up and
* its nlookup should not be incremented. fuse_iget() does

15
fs/fuse/readdir.c
View File

@ -149,7 +149,7 @@ static int parse_dirfile(char *buf, size_t nbytes, struct file *file,
static int fuse_direntplus_link(struct file *file,
struct fuse_direntplus *direntplus,
u64 attr_version)
u64 attr_version, u64 evict_ctr)
{
struct fuse_entry_out *o = &direntplus->entry_out;
struct fuse_dirent *dirent = &direntplus->dirent;
@ -233,7 +233,7 @@ static int fuse_direntplus_link(struct file *file,
} else {
inode = fuse_iget(dir->i_sb, o->nodeid, o->generation,
&o->attr, ATTR_TIMEOUT(o),
attr_version);
attr_version, evict_ctr);
if (!inode)
inode = ERR_PTR(-ENOMEM);
@ -284,7 +284,8 @@ static void fuse_force_forget(struct file *file, u64 nodeid)
}
static int parse_dirplusfile(char *buf, size_t nbytes, struct file *file,
struct dir_context *ctx, u64 attr_version)
struct dir_context *ctx, u64 attr_version,
u64 evict_ctr)
{
struct fuse_direntplus *direntplus;
struct fuse_dirent *dirent;
@ -319,7 +320,7 @@ static int parse_dirplusfile(char *buf, size_t nbytes, struct file *file,
buf += reclen;
nbytes -= reclen;
ret = fuse_direntplus_link(file, direntplus, attr_version);
ret = fuse_direntplus_link(file, direntplus, attr_version, evict_ctr);
if (ret)
fuse_force_forget(file, direntplus->entry_out.nodeid);
}
@ -337,7 +338,7 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
struct fuse_io_args ia = {};
struct fuse_args_pages *ap = &ia.ap;
struct fuse_folio_desc desc = { .length = PAGE_SIZE };
u64 attr_version = 0;
u64 attr_version = 0, evict_ctr = 0;
bool locked;
folio = folio_alloc(GFP_KERNEL, 0);
@ -351,6 +352,7 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
ap->descs = &desc;
if (plus) {
attr_version = fuse_get_attr_version(fm->fc);
evict_ctr = fuse_get_evict_ctr(fm->fc);
fuse_read_args_fill(&ia, file, ctx->pos, PAGE_SIZE,
FUSE_READDIRPLUS);
} else {
@ -368,7 +370,8 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
fuse_readdir_cache_end(file, ctx->pos);
} else if (plus) {
res = parse_dirplusfile(folio_address(folio), res,
file, ctx, attr_version);
file, ctx, attr_version,
evict_ctr);
} else {
res = parse_dirfile(folio_address(folio), res, file,
ctx);