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debugfs: don't mess with bits in ->d_fsdata

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The reason we need that crap is the dual use ->d_fsdata has there -
it's both holding a debugfs_fsdata reference after the first
debugfs_file_get() (actually, after the call of proxy ->open())
*and* it serves as a place to stash a reference to real file_operations
from object creation to the first open.  Oh, and it's triple use,
actually - that stashed reference might be to debugfs_short_fops.

Bugger that for a game of solidiers - just put the operations
reference into debugfs-private augmentation of inode.  And split
debugfs_full_file_operations into full and short cases, so that
debugfs_get_file() could tell one from another.

Voila - ->d_fsdata holds NULL until the first (successful) debugfs_get_file()
and a reference to struct debugfs_fsdata afterwards.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20250112080705.141166-4-viro@zeniv.linux.org.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Al Viro
2025-01-12 08:06:48 +00:00
committed by Greg Kroah-Hartman
parent 41a0ecc099
commit 95688800ee
3 changed files with 38 additions and 61 deletions
Download Patch File Download Diff File Expand all files Collapse all files
fs/debugfs/file.c
+28 -30
View File
@@ -51,7 +51,7 @@ const struct file_operations *debugfs_real_fops(const struct file *filp)
{
struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata;
if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT) {
if (!fsd) {
/*
* Urgh, we've been called w/o a protecting
* debugfs_file_get().
@@ -84,9 +84,11 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
return -EINVAL;
d_fsd = READ_ONCE(dentry->d_fsdata);
if (!((unsigned long)d_fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)) {
if (d_fsd) {
fsd = d_fsd;
} else {
struct inode *inode = dentry->d_inode;
if (WARN_ON(mode == DBGFS_GET_ALREADY))
return -EINVAL;
@@ -96,9 +98,7 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
if (mode == DBGFS_GET_SHORT) {
const struct debugfs_short_fops *ops;
ops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
fsd->short_fops = ops;
ops = fsd->short_fops = DEBUGFS_I(inode)->short_fops;
if (ops->llseek)
fsd->methods |= HAS_LSEEK;
if (ops->read)
@@ -107,9 +107,7 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
fsd->methods |= HAS_WRITE;
} else {
const struct file_operations *ops;
ops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
fsd->real_fops = ops;
ops = fsd->real_fops = DEBUGFS_I(inode)->real_fops;
if (ops->llseek)
fsd->methods |= HAS_LSEEK;
if (ops->read)
@@ -126,10 +124,11 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
INIT_LIST_HEAD(&fsd->cancellations);
mutex_init(&fsd->cancellations_mtx);
if (cmpxchg(&dentry->d_fsdata, d_fsd, fsd) != d_fsd) {
d_fsd = cmpxchg(&dentry->d_fsdata, NULL, fsd);
if (d_fsd) {
mutex_destroy(&fsd->cancellations_mtx);
kfree(fsd);
fsd = READ_ONCE(dentry->d_fsdata);
fsd = d_fsd;
}
}
@@ -226,8 +225,7 @@ void debugfs_enter_cancellation(struct file *file,
return;
fsd = READ_ONCE(dentry->d_fsdata);
if (WARN_ON(!fsd ||
((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
if (WARN_ON(!fsd))
return;
mutex_lock(&fsd->cancellations_mtx);
@@ -258,8 +256,7 @@ void debugfs_leave_cancellation(struct file *file,
return;
fsd = READ_ONCE(dentry->d_fsdata);
if (WARN_ON(!fsd ||
((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
if (WARN_ON(!fsd))
return;
mutex_lock(&fsd->cancellations_mtx);
@@ -427,22 +424,21 @@ static int full_proxy_release(struct inode *inode, struct file *filp)
* not to leak any resources. Releasers must not assume that
* ->i_private is still being meaningful here.
*/
if (real_fops && real_fops->release)
if (real_fops->release)
r = real_fops->release(inode, filp);
fops_put(real_fops);
return r;
}
static int full_proxy_open(struct inode *inode, struct file *filp,
enum dbgfs_get_mode mode)
static int full_proxy_open_regular(struct inode *inode, struct file *filp)
{
struct dentry *dentry = F_DENTRY(filp);
const struct file_operations *real_fops;
struct debugfs_fsdata *fsd;
int r;
r = __debugfs_file_get(dentry, mode);
r = __debugfs_file_get(dentry, DBGFS_GET_REGULAR);
if (r)
return r == -EIO ? -ENOENT : r;
@@ -452,7 +448,7 @@ static int full_proxy_open(struct inode *inode, struct file *filp,
if (r)
goto out;
if (real_fops && !fops_get(real_fops)) {
if (!fops_get(real_fops)) {
#ifdef CONFIG_MODULES
if (real_fops->owner &&
real_fops->owner->state == MODULE_STATE_GOING) {
@@ -468,11 +464,8 @@ static int full_proxy_open(struct inode *inode, struct file *filp,
goto out;
}
if (!real_fops || real_fops->open) {
if (real_fops)
r = real_fops->open(inode, filp);
else
r = simple_open(inode, filp);
if (real_fops->open) {
r = real_fops->open(inode, filp);
if (r) {
fops_put(real_fops);
} else if (filp->f_op != &debugfs_full_proxy_file_operations) {
@@ -487,11 +480,6 @@ out:
return r;
}
static int full_proxy_open_regular(struct inode *inode, struct file *filp)
{
return full_proxy_open(inode, filp, DBGFS_GET_REGULAR);
}
const struct file_operations debugfs_full_proxy_file_operations = {
.open = full_proxy_open_regular,
.release = full_proxy_release,
@@ -504,7 +492,17 @@ const struct file_operations debugfs_full_proxy_file_operations = {
static int full_proxy_open_short(struct inode *inode, struct file *filp)
{
return full_proxy_open(inode, filp, DBGFS_GET_SHORT);
struct dentry *dentry = F_DENTRY(filp);
int r;
r = __debugfs_file_get(dentry, DBGFS_GET_SHORT);
if (r)
return r == -EIO ? -ENOENT : r;
r = debugfs_locked_down(inode, filp, NULL);
if (!r)
r = simple_open(inode, filp);
debugfs_file_put(dentry);
return r;
}
const struct file_operations debugfs_full_short_proxy_file_operations = {
fs/debugfs/inode.c
+7 -22
View File
@@ -243,15 +243,10 @@ static void debugfs_release_dentry(struct dentry *dentry)
{
struct debugfs_fsdata *fsd = dentry->d_fsdata;
if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
return;
/* check it wasn't a dir or automount (no fsdata) */
if (fsd) {
WARN_ON(!list_empty(&fsd->cancellations));
mutex_destroy(&fsd->cancellations_mtx);
}
kfree(fsd);
}
@@ -459,9 +454,10 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
inode->i_private = data;
inode->i_op = &debugfs_file_inode_operations;
if (!real_fops)
proxy_fops = &debugfs_noop_file_operations;
inode->i_fop = proxy_fops;
dentry->d_fsdata = (void *)((unsigned long)real_fops |
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
DEBUGFS_I(inode)->raw = real_fops;
d_instantiate(dentry, inode);
fsnotify_create(d_inode(dentry->d_parent), dentry);
@@ -472,13 +468,8 @@ struct dentry *debugfs_create_file_full(const char *name, umode_t mode,
struct dentry *parent, void *data,
const struct file_operations *fops)
{
if (WARN_ON((unsigned long)fops &
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
return ERR_PTR(-EINVAL);
return __debugfs_create_file(name, mode, parent, data,
fops ? &debugfs_full_proxy_file_operations :
&debugfs_noop_file_operations,
&debugfs_full_proxy_file_operations,
fops);
}
EXPORT_SYMBOL_GPL(debugfs_create_file_full);
@@ -487,13 +478,8 @@ struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
struct dentry *parent, void *data,
const struct debugfs_short_fops *fops)
{
if (WARN_ON((unsigned long)fops &
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
return ERR_PTR(-EINVAL);
return __debugfs_create_file(name, mode, parent, data,
fops ? &debugfs_full_short_proxy_file_operations :
&debugfs_noop_file_operations,
&debugfs_full_short_proxy_file_operations,
fops);
}
EXPORT_SYMBOL_GPL(debugfs_create_file_short);
@@ -531,8 +517,7 @@ struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
{
return __debugfs_create_file(name, mode, parent, data,
fops ? &debugfs_open_proxy_file_operations :
&debugfs_noop_file_operations,
&debugfs_open_proxy_file_operations,
fops);
}
EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
@@ -737,7 +722,7 @@ static void __debugfs_file_removed(struct dentry *dentry)
*/
smp_mb();
fsd = READ_ONCE(dentry->d_fsdata);
if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
if (!fsd)
return;
/* if this was the last reference, we're done */
fs/debugfs/internal.h
+3 -9
View File
@@ -14,6 +14,9 @@ struct file_operations;
struct debugfs_inode_info {
struct inode vfs_inode;
union {
const void *raw;
const struct file_operations *real_fops;
const struct debugfs_short_fops *short_fops;
debugfs_automount_t automount;
};
};
@@ -51,15 +54,6 @@ enum {
HAS_IOCTL = 16
};
/*
* A dentry's ->d_fsdata either points to the real fops or to a
* dynamically allocated debugfs_fsdata instance.
* In order to distinguish between these two cases, a real fops
* pointer gets its lowest bit set.
*/
#define DEBUGFS_FSDATA_IS_REAL_FOPS_BIT BIT(0)
/* Access BITS */
#define DEBUGFS_ALLOW_API BIT(0)
#define DEBUGFS_ALLOW_MOUNT BIT(1)