[PATCH RFC 09/27] smb: client: let procfs copy in writes

From: Christian Brauner <brauner@kernel.org>
Date: 2026-11-02 15:22:52
Also in: dri-devel, kexec, linux-acpi, linux-alpha, linux-cifs, linux-doc, linux-ext4, linux-fbdev, linux-fsdevel, linux-hwmon, linux-input, linux-kselftest, linux-m68k, linux-mm, linux-modules, linux-nfs, linux-pci, linux-raid, linux-s390, linux-scsi, linux-serial, linux-sh, linux-sound, linux-um, linux-usb, linux-wireless, linuxppc-dev, lkml, netfilter-devel, ntfs3, platform-driver-x86, sparclinux
Reply to: Christian Brauner, 2026-11-02

Implement ->proc_write_buf() for the files in /proc/fs/cifs so procfs
copies in what is written before it pins the entry, and parse what was
written from that copy. Writes larger than PAGE_SIZE - 1 bytes fail with
-EINVAL now, SecurityFlags never took more than 11 bytes. Empty writes
to cifsFYI and dfscache fail with -EINVAL too, they looked at a byte
that wasn't written before. kstrtoint_from_user() looked at the first
34 bytes of a write to cifs_debug_dirs and the smbdirect files, now the
whole write is parsed.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/smb/client/cifs_debug.c | 62 +++++++++++++++++++---------------------------
 fs/smb/client/dfs_cache.c  | 13 +++-------
 2 files changed, 29 insertions(+), 46 deletions(-)

diff --git a/fs/smb/client/cifs_debug.c b/fs/smb/client/cifs_debug.c
index 664072ab3342..fb1323bf44c7 100644
--- a/fs/smb/client/cifs_debug.c
+++ b/fs/smb/client/cifs_debug.c

@@ -359,12 +359,12 @@ static int cifs_debug_dirs_proc_show(struct seq_file *m, void *v)
 #ifdef CONFIG_CIFS_DEBUG
 
 /* Drop all cached directory entries across all CIFS mounts. */
-static ssize_t cifs_debug_dirs_proc_write(struct file *file, const char __user *buffer,
+static ssize_t cifs_debug_dirs_proc_write(struct file *file, char *buffer,
 					  size_t count, loff_t *ppos)
 {
 	int rc, v;
 
-	rc = kstrtoint_from_user(buffer, count, 10, &v);
+	rc = kstrtoint(buffer, 10, &v);
 	if (rc)
 		return rc;

@@ -390,7 +390,7 @@ static ssize_t cifs_debug_dirs_proc_write(struct file *file, const char __user *
 
 static const struct proc_ops cifs_debug_dirs_proc_ops = {
 	.proc_show	= cifs_debug_dirs_proc_show,
-	.proc_write	= cifs_debug_dirs_proc_write,
+	.proc_write_buf	= cifs_debug_dirs_proc_write,
 };
 #endif /* CONFIG_CIFS_DEBUG */

@@ -713,8 +713,8 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t cifs_stats_proc_write(struct file *file,
-		const char __user *buffer, size_t count, loff_t *ppos)
+static ssize_t cifs_stats_proc_write(struct file *file, char *buffer,
+		size_t count, loff_t *ppos)
 {
 	bool bv;
 	int rc;

@@ -722,7 +722,7 @@ static ssize_t cifs_stats_proc_write(struct file *file,
 	struct cifs_ses *ses;
 	struct cifs_tcon *tcon;
 
-	rc = kstrtobool_from_user(buffer, count, &bv);
+	rc = kstrtobool(buffer, &bv);
 	if (rc == 0) {
 #ifdef CONFIG_CIFS_STATS2
 		int i;

@@ -854,16 +854,16 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 
 static const struct proc_ops cifs_stats_proc_ops = {
 	.proc_show	= cifs_stats_proc_show,
-	.proc_write	= cifs_stats_proc_write,
+	.proc_write_buf	= cifs_stats_proc_write,
 };
 
 #ifdef CONFIG_CIFS_SMB_DIRECT
 #define PROC_FILE_DEFINE(name) \
-static ssize_t name##_write(struct file *file, const char __user *buffer, \
+static ssize_t name##_write(struct file *file, char *buffer, \
 	size_t count, loff_t *ppos) \
 { \
 	int rc; \
-	rc = kstrtoint_from_user(buffer, count, 10, &name); \
+	rc = kstrtoint(buffer, 10, &name); \
 	if (rc) \
 		return rc; \
 	return count; \

@@ -876,7 +876,7 @@ static int name##_proc_show(struct seq_file *m, void *v) \
 \
 static const struct proc_ops cifs_##name##_proc_fops = { \
 	.proc_show	= name##_proc_show, \
-	.proc_write	= name##_write, \
+	.proc_write_buf	= name##_write, \
 }
 
 PROC_FILE_DEFINE(rdma_readwrite_threshold);

@@ -990,16 +990,12 @@ static int cifsFYI_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t cifsFYI_proc_write(struct file *file, const char __user *buffer,
+static ssize_t cifsFYI_proc_write(struct file *file, char *buffer,
 		size_t count, loff_t *ppos)
 {
-	char c[2] = { '\0' };
+	char c[2] = { buffer[0] };
 	bool bv;
-	int rc;
 
-	rc = get_user(c[0], buffer);
-	if (rc)
-		return rc;
 	if (kstrtobool(c, &bv) == 0)
 		cifsFYI = bv;
 	else if ((c[0] > '1') && (c[0] <= '9'))

@@ -1012,7 +1008,7 @@ static ssize_t cifsFYI_proc_write(struct file *file, const char __user *buffer,
 
 static const struct proc_ops cifsFYI_proc_ops = {
 	.proc_show	= cifsFYI_proc_show,
-	.proc_write	= cifsFYI_proc_write,
+	.proc_write_buf	= cifsFYI_proc_write,
 };
 
 static int cifs_linux_ext_proc_show(struct seq_file *m, void *v)

@@ -1021,12 +1017,12 @@ static int cifs_linux_ext_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t cifs_linux_ext_proc_write(struct file *file,
-		const char __user *buffer, size_t count, loff_t *ppos)
+static ssize_t cifs_linux_ext_proc_write(struct file *file, char *buffer,
+		size_t count, loff_t *ppos)
 {
 	int rc;
 
-	rc = kstrtobool_from_user(buffer, count, &linuxExtEnabled);
+	rc = kstrtobool(buffer, &linuxExtEnabled);
 	if (rc)
 		return rc;

@@ -1035,7 +1031,7 @@ static ssize_t cifs_linux_ext_proc_write(struct file *file,
 
 static const struct proc_ops cifs_linux_ext_proc_ops = {
 	.proc_show	= cifs_linux_ext_proc_show,
-	.proc_write	= cifs_linux_ext_proc_write,
+	.proc_write_buf	= cifs_linux_ext_proc_write,
 };
 
 static int cifs_lookup_cache_proc_show(struct seq_file *m, void *v)

@@ -1044,12 +1040,12 @@ static int cifs_lookup_cache_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t cifs_lookup_cache_proc_write(struct file *file,
-		const char __user *buffer, size_t count, loff_t *ppos)
+static ssize_t cifs_lookup_cache_proc_write(struct file *file, char *buffer,
+		size_t count, loff_t *ppos)
 {
 	int rc;
 
-	rc = kstrtobool_from_user(buffer, count, &lookupCacheEnabled);
+	rc = kstrtobool(buffer, &lookupCacheEnabled);
 	if (rc)
 		return rc;

@@ -1058,7 +1054,7 @@ static ssize_t cifs_lookup_cache_proc_write(struct file *file,
 
 static const struct proc_ops cifs_lookup_cache_proc_ops = {
 	.proc_show	= cifs_lookup_cache_proc_show,
-	.proc_write	= cifs_lookup_cache_proc_write,
+	.proc_write_buf	= cifs_lookup_cache_proc_write,
 };
 
 static int traceSMB_proc_show(struct seq_file *m, void *v)

@@ -1067,12 +1063,12 @@ static int traceSMB_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t traceSMB_proc_write(struct file *file, const char __user *buffer,
+static ssize_t traceSMB_proc_write(struct file *file, char *buffer,
 		size_t count, loff_t *ppos)
 {
 	int rc;
 
-	rc = kstrtobool_from_user(buffer, count, &traceSMB);
+	rc = kstrtobool(buffer, &traceSMB);
 	if (rc)
 		return rc;

@@ -1081,7 +1077,7 @@ static ssize_t traceSMB_proc_write(struct file *file, const char __user *buffer,
 
 static const struct proc_ops traceSMB_proc_ops = {
 	.proc_show	= traceSMB_proc_show,
-	.proc_write	= traceSMB_proc_write,
+	.proc_write_buf	= traceSMB_proc_write,
 };
 
 static int cifs_security_flags_proc_show(struct seq_file *m, void *v)

@@ -1111,21 +1107,15 @@ cifs_security_flags_handle_must_flags(unsigned int *flags)
 }
 
 static ssize_t cifs_security_flags_proc_write(struct file *file,
-		const char __user *buffer, size_t count, loff_t *ppos)
+		char *flags_string, size_t count, loff_t *ppos)
 {
 	int rc;
 	unsigned int flags;
-	char flags_string[12];
 	bool bv;
 
 	if ((count < 1) || (count > 11))
 		return -EINVAL;
 
-	memset(flags_string, 0, sizeof(flags_string));
-
-	if (copy_from_user(flags_string, buffer, count))
-		return -EFAULT;
-
 	if (count < 3) {
 		/* single char or single char followed by null */
 		if (kstrtobool(flags_string, &bv) == 0) {

@@ -1176,7 +1166,7 @@ static ssize_t cifs_security_flags_proc_write(struct file *file,
 
 static const struct proc_ops cifs_security_flags_proc_ops = {
 	.proc_show	= cifs_security_flags_proc_show,
-	.proc_write	= cifs_security_flags_proc_write,
+	.proc_write_buf	= cifs_security_flags_proc_write,
 };
 
 /* To make it easier to debug, can help to show mount params */

diff --git a/fs/smb/client/dfs_cache.c b/fs/smb/client/dfs_cache.c
index 58f16cf83d36..a6aa05430b15 100644
--- a/fs/smb/client/dfs_cache.c
+++ b/fs/smb/client/dfs_cache.c

@@ -191,17 +191,10 @@ static int dfscache_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static ssize_t dfscache_proc_write(struct file *file, const char __user *buffer,
+static ssize_t dfscache_proc_write(struct file *file, char *buffer,
 				   size_t count, loff_t *ppos)
 {
-	char c;
-	int rc;
-
-	rc = get_user(c, buffer);
-	if (rc)
-		return rc;
-
-	if (c != '0')
+	if (buffer[0] != '0')
 		return -EINVAL;
 
 	cifs_dbg(FYI, "clearing dfs cache\n");

@@ -215,7 +208,7 @@ static ssize_t dfscache_proc_write(struct file *file, const char __user *buffer,
 
 const struct proc_ops dfscache_proc_ops = {
 	.proc_show	= dfscache_proc_show,
-	.proc_write	= dfscache_proc_write,
+	.proc_write_buf	= dfscache_proc_write,
 };
 
 #ifdef CONFIG_CIFS_DEBUG2

-- 
2.53.0

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