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* [PATCH v3 0/2] vfs: fix a mount table handling problem
@ 2022-07-25  1:17 Ian Kent
  2022-07-25  1:17 ` [PATCH v3 1/2] ext4: fix possible null pointer dereference Ian Kent
  2022-07-25  1:17 ` [PATCH v3 2/2] vfs: parse: deal with zero length string value Ian Kent
  0 siblings, 2 replies; 3+ messages in thread
From: Ian Kent @ 2022-07-25  1:17 UTC (permalink / raw)
  To: Al Viro
  Cc: Andrew Morton, Siddhesh Poyarekar, David Howells, Miklos Szeredi,
	Carlos Maiolino, linux-fsdevel, Kernel Mailing List

Whenever a mount has an empty "source" (aka mnt_fsname), the glibc
function getmntent incorrectly parses its input, resulting in reporting
incorrect data to the caller.

The problem is that the get_mnt_entry() function in glibc's
misc/mntent_r.c assumes that leading whitespace on a line can always
be discarded because it will always be followed by a # for the case
of a comment or a non-whitespace character that's part of the value
of the first field. However, this assumption is violated when the
value of the first field is an empty string.

This is fixed in the mount API code by simply checking for a pointer
that contains a NULL and treating it as a NULL pointer.

Changes:

v3: added patch to fix zero length string access violation caused after
    fs parser patch is applied.

v2: fix possible oops if conversion functions such as fs_param_is_u32()
    are called.

Signed-off-by: Ian Kent <raven@themaw.net>
---

Ian Kent (2):
      ext4: fix possible null pointer dereference
      vfs: parse: deal with zero length string value


 fs/ext4/super.c            |  4 ++--
 fs/fs_context.c            | 17 ++++++++++++-----
 fs/fs_parser.c             | 16 ++++++++++++++++
 include/linux/fs_context.h |  3 ++-
 4 files changed, 32 insertions(+), 8 deletions(-)

--
Ian


^ permalink raw reply	[flat|nested] 3+ messages in thread
* [PATCH v3 1/2] ext4: fix possible null pointer dereference
  2022-07-25  1:17 [PATCH v3 0/2] vfs: fix a mount table handling problem Ian Kent
@ 2022-07-25  1:17 ` Ian Kent
  2022-07-25  1:17 ` [PATCH v3 2/2] vfs: parse: deal with zero length string value Ian Kent
  1 sibling, 0 replies; 3+ messages in thread
From: Ian Kent @ 2022-07-25  1:17 UTC (permalink / raw)
  To: Al Viro
  Cc: Andrew Morton, Siddhesh Poyarekar, David Howells, Miklos Szeredi,
	Carlos Maiolino, linux-fsdevel, Kernel Mailing List

It could be the case that the file system parameter ->string value is
NULL rather than a zero length string.

Guard against this possibility in ext4_parse_param().

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Ian Kent <raven@themaw.net>
---
 fs/ext4/super.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 845f2f8aee5f..97160e982ced 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2110,12 +2110,12 @@ static int ext4_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	switch (token) {
 #ifdef CONFIG_QUOTA
 	case Opt_usrjquota:
-		if (!*param->string)
+		if (!param->string || !*param->string)
 			return unnote_qf_name(fc, USRQUOTA);
 		else
 			return note_qf_name(fc, USRQUOTA, param);
 	case Opt_grpjquota:
-		if (!*param->string)
+		if (!param->string || !*param->string)
 			return unnote_qf_name(fc, GRPQUOTA);
 		else
 			return note_qf_name(fc, GRPQUOTA, param);



^ permalink raw reply related	[flat|nested] 3+ messages in thread
* [PATCH v3 2/2] vfs: parse: deal with zero length string value
  2022-07-25  1:17 [PATCH v3 0/2] vfs: fix a mount table handling problem Ian Kent
  2022-07-25  1:17 ` [PATCH v3 1/2] ext4: fix possible null pointer dereference Ian Kent
@ 2022-07-25  1:17 ` Ian Kent
  1 sibling, 0 replies; 3+ messages in thread
From: Ian Kent @ 2022-07-25  1:17 UTC (permalink / raw)
  To: Al Viro
  Cc: Andrew Morton, Siddhesh Poyarekar, David Howells, Miklos Szeredi,
	Carlos Maiolino, linux-fsdevel, Kernel Mailing List

Parsing an fs string that has zero length should result in the parameter
being set to NULL so that downstream processing handles it correctly.
For example, the proc mount table processing should print "(none)" in
this case to preserve mount record field count, but if the value points
to the NULL string this doesn't happen.

Changes:

v2: fix possible oops if conversion functions such as fs_param_is_u32()
    are called.

Signed-off-by: Ian Kent <raven@themaw.net>
---
 fs/fs_context.c            |   17 ++++++++++++-----
 fs/fs_parser.c             |   16 ++++++++++++++++
 include/linux/fs_context.h |    3 ++-
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 24ce12f0db32..df04e5fc6d66 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -96,7 +96,9 @@ int vfs_parse_fs_param_source(struct fs_context *fc, struct fs_parameter *param)
 	if (strcmp(param->key, "source") != 0)
 		return -ENOPARAM;
 
-	if (param->type != fs_value_is_string)
+	/* source value may be NULL */
+	if (param->type != fs_value_is_string &&
+	    param->type != fs_value_is_empty)
 		return invalf(fc, "Non-string source");
 
 	if (fc->source)
@@ -175,10 +177,15 @@ int vfs_parse_fs_string(struct fs_context *fc, const char *key,
 	};
 
 	if (value) {
-		param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
-		if (!param.string)
-			return -ENOMEM;
-		param.type = fs_value_is_string;
+		if (!v_size) {
+			param.string = NULL;
+			param.type = fs_value_is_empty;
+		} else {
+			param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
+			if (!param.string)
+				return -ENOMEM;
+			param.type = fs_value_is_string;
+		}
 	}
 
 	ret = vfs_parse_fs_param(fc, &param);
diff --git a/fs/fs_parser.c b/fs/fs_parser.c
index ed40ce5742fd..2046f41ab00b 100644
--- a/fs/fs_parser.c
+++ b/fs/fs_parser.c
@@ -197,6 +197,8 @@ int fs_param_is_bool(struct p_log *log, const struct fs_parameter_spec *p,
 		     struct fs_parameter *param, struct fs_parse_result *result)
 {
 	int b;
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string)
 		return fs_param_bad_value(log, param);
 	if (!*param->string && (p->flags & fs_param_can_be_empty))
@@ -213,6 +215,8 @@ int fs_param_is_u32(struct p_log *log, const struct fs_parameter_spec *p,
 		    struct fs_parameter *param, struct fs_parse_result *result)
 {
 	int base = (unsigned long)p->data;
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string)
 		return fs_param_bad_value(log, param);
 	if (!*param->string && (p->flags & fs_param_can_be_empty))
@@ -226,6 +230,8 @@ EXPORT_SYMBOL(fs_param_is_u32);
 int fs_param_is_s32(struct p_log *log, const struct fs_parameter_spec *p,
 		    struct fs_parameter *param, struct fs_parse_result *result)
 {
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string)
 		return fs_param_bad_value(log, param);
 	if (!*param->string && (p->flags & fs_param_can_be_empty))
@@ -239,6 +245,8 @@ EXPORT_SYMBOL(fs_param_is_s32);
 int fs_param_is_u64(struct p_log *log, const struct fs_parameter_spec *p,
 		    struct fs_parameter *param, struct fs_parse_result *result)
 {
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string)
 		return fs_param_bad_value(log, param);
 	if (!*param->string && (p->flags & fs_param_can_be_empty))
@@ -253,6 +261,8 @@ int fs_param_is_enum(struct p_log *log, const struct fs_parameter_spec *p,
 		     struct fs_parameter *param, struct fs_parse_result *result)
 {
 	const struct constant_table *c;
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string)
 		return fs_param_bad_value(log, param);
 	if (!*param->string && (p->flags & fs_param_can_be_empty))
@@ -268,6 +278,8 @@ EXPORT_SYMBOL(fs_param_is_enum);
 int fs_param_is_string(struct p_log *log, const struct fs_parameter_spec *p,
 		       struct fs_parameter *param, struct fs_parse_result *result)
 {
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_string ||
 	    (!*param->string && !(p->flags & fs_param_can_be_empty)))
 		return fs_param_bad_value(log, param);
@@ -278,6 +290,8 @@ EXPORT_SYMBOL(fs_param_is_string);
 int fs_param_is_blob(struct p_log *log, const struct fs_parameter_spec *p,
 		     struct fs_parameter *param, struct fs_parse_result *result)
 {
+	if (param->type == fs_value_is_empty)
+		return 0;
 	if (param->type != fs_value_is_blob)
 		return fs_param_bad_value(log, param);
 	return 0;
@@ -287,6 +301,8 @@ EXPORT_SYMBOL(fs_param_is_blob);
 int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p,
 		  struct fs_parameter *param, struct fs_parse_result *result)
 {
+	if (param->type == fs_value_is_empty)
+		return 0;
 	switch (param->type) {
 	case fs_value_is_string:
 		if ((!*param->string && !(p->flags & fs_param_can_be_empty)) ||
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 13fa6f3df8e4..ff1375a16c8c 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -50,7 +50,8 @@ enum fs_context_phase {
  */
 enum fs_value_type {
 	fs_value_is_undefined,
-	fs_value_is_flag,		/* Value not given a value */
+	fs_value_is_flag,		/* Does not take a value */
+	fs_value_is_empty,		/* Value is not given */
 	fs_value_is_string,		/* Value is a string */
 	fs_value_is_blob,		/* Value is a binary blob */
 	fs_value_is_filename,		/* Value is a filename* + dirfd */



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2022-07-25  1:17 [PATCH v3 0/2] vfs: fix a mount table handling problem Ian Kent
2022-07-25  1:17 ` [PATCH v3 1/2] ext4: fix possible null pointer dereference Ian Kent
2022-07-25  1:17 ` [PATCH v3 2/2] vfs: parse: deal with zero length string value Ian Kent

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