superrob1500
/
mirror-linux
mirror of https://github.com/torvalds/linux
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

smack: fix bug: setting task label silently ignores input garbage 

This command:
    # echo foo/bar >/proc/$$/attr/smack/current

gives the task a label 'foo' w/o indication
that label does not match input.
Setting the label with lsm_set_self_attr() syscall
behaves identically.

This occures because:

1) smk_parse_smack() is used to convert input to a label
2) smk_parse_smack() takes only that part from the
   beginning of the input that looks like a label.
3) `/' is prohibited in labels, so only "foo" is taken.

(2) is by design, because smk_parse_smack() is used
for parsing strings which are more than just a label.

Silent failure is not a good thing, and there are two
indicators that this was not done intentionally:

    (size >= SMK_LONGLABEL) ~> invalid

clause at the beginning of the do_setattr() and the
"Returns the length of the smack label" claim
in the do_setattr() description.

So I fixed this by adding one tiny check:
the taken label length == input length.

Since input length is now strictly controlled,
I changed the two ways of setting label

   smack_setselfattr(): lsm_set_self_attr() syscall
   smack_setprocattr(): > /proc/.../current

to accommodate the divergence in
what they understand by "input length":

  smack_setselfattr counts mandatory \0 into input length,
  smack_setprocattr does not.

  smack_setprocattr allows various trailers after label

Related changes:

* fixed description for smk_parse_smack

* allow unprivileged tasks validate label syntax.

* extract smk_parse_label_len() from smk_parse_smack()
  so parsing may be done w/o string allocation.

* extract smk_import_valid_label() from smk_import_entry()
  to avoid repeated parsing.

* smk_parse_smack(): scan null-terminated strings
  for no more than SMK_LONGLABEL(256) characters

* smack_setselfattr(): require struct lsm_ctx . flags == 0
  to reserve them for future.

Fixes: e114e47377 ("Smack: Simplified Mandatory Access Control Kernel")
Signed-off-by: Konstantin Andreev <andreev@swemel.ru>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
pull/1279/head
Konstantin Andreev 2025-06-17 00:32:17 +03:00 committed by Casey Schaufler
parent c147e13ea7
commit 674e2b2479
4 changed files with 157 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
Documentation/admin-guide/LSM/Smack.rst
View File

@ -601,10 +601,15 @@ specification.
Task Attribute
~~~~~~~~~~~~~~
The Smack label of a process can be read from /proc/<pid>/attr/current. A
process can read its own Smack label from /proc/self/attr/current. A
The Smack label of a process can be read from ``/proc/<pid>/attr/current``. A
process can read its own Smack label from ``/proc/self/attr/current``. A
privileged process can change its own Smack label by writing to
/proc/self/attr/current but not the label of another process.
``/proc/self/attr/current`` but not the label of another process.
Format of writing is : only the label or the label followed by one of the
3 trailers: ``\n`` (by common agreement for ``/proc/...`` interfaces),
``\0`` (because some applications incorrectly include it),
``\n\0`` (because we think some applications may incorrectly include it).
File Attribute
~~~~~~~~~~~~~~

3
security/smack/smack.h
View File

@ -286,9 +286,12 @@ int smk_tskacc(struct task_smack *, struct smack_known *,
int smk_curacc(struct smack_known *, u32, struct smk_audit_info *);
int smack_str_from_perm(char *string, int access);
struct smack_known *smack_from_secid(const u32);
int smk_parse_label_len(const char *string, int len);
char *smk_parse_smack(const char *string, int len);
int smk_netlbl_mls(int, char *, struct netlbl_lsm_secattr *, int);
struct smack_known *smk_import_entry(const char *, int);
struct smack_known *smk_import_valid_label(const char *label, int label_len,
gfp_t gfp);
void smk_insert_entry(struct smack_known *skp);
struct smack_known *smk_find_entry(const char *);
bool smack_privileged(int cap);

93
security/smack/smack_access.c
View File

@ -443,19 +443,19 @@ struct smack_known *smk_find_entry(const char *string)
}
/**
* smk_parse_smack - parse smack label from a text string
* @string: a text string that might contain a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
* smk_parse_label_len - calculate the length of the starting segment
* in the string that constitutes a valid smack label
* @string: a text string that might contain a Smack label at the beginning
* @len: the maximum size to look into, may be zero if string is null-terminated
*
* Returns a pointer to the clean label or an error code.
* Returns the length of the segment (0 < L < SMK_LONGLABEL) or an error code.
*/
char *smk_parse_smack(const char *string, int len)
int smk_parse_label_len(const char *string, int len)
{
char *smack;
int i;
if (len <= 0)
len = strlen(string) + 1;
if (len <= 0 || len > SMK_LONGLABEL)
len = SMK_LONGLABEL;
/*
* Reserve a leading '-' as an indicator that
@ -463,7 +463,7 @@ char *smk_parse_smack(const char *string, int len)
* including /smack/cipso and /smack/cipso2
*/
if (string[0] == '-')
return ERR_PTR(-EINVAL);
return -EINVAL;
for (i = 0; i < len; i++)
if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
@ -471,6 +471,25 @@ char *smk_parse_smack(const char *string, int len)
break;
if (i == 0 || i >= SMK_LONGLABEL)
return -EINVAL;
return i;
}
/**
* smk_parse_smack - copy the starting segment in the string
* that constitutes a valid smack label
* @string: a text string that might contain a Smack label at the beginning
* @len: the maximum size to look into, may be zero if string is null-terminated
*
* Returns a pointer to the copy of the label or an error code.
*/
char *smk_parse_smack(const char *string, int len)
{
char *smack;
int i = smk_parse_label_len(string, len);
if (i < 0)
return ERR_PTR(-EINVAL);
smack = kstrndup(string, i, GFP_NOFS);
@ -554,31 +573,25 @@ int smack_populate_secattr(struct smack_known *skp)
}
/**
* smk_import_entry - import a label, return the list entry
* @string: a text string that might be a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
* smk_import_valid_allocated_label - import a label, return the list entry
* @smack: a text string that is a valid Smack label and may be kfree()ed.
* It is consumed: either becomes a part of the entry or kfree'ed.
*
* Returns a pointer to the entry in the label list that
* matches the passed string, adding it if necessary,
* or an error code.
* Returns: see description of smk_import_entry()
*/
struct smack_known *smk_import_entry(const char *string, int len)
static struct smack_known *
smk_import_allocated_label(char *smack, gfp_t gfp)
{
struct smack_known *skp;
char *smack;
int rc;
smack = smk_parse_smack(string, len);
if (IS_ERR(smack))
return ERR_CAST(smack);
mutex_lock(&smack_known_lock);
skp = smk_find_entry(smack);
if (skp != NULL)
goto freeout;
skp = kzalloc(sizeof(*skp), GFP_NOFS);
skp = kzalloc(sizeof(*skp), gfp);
if (skp == NULL) {
skp = ERR_PTR(-ENOMEM);
goto freeout;
@ -608,6 +621,42 @@ unlockout:
return skp;
}
/**
* smk_import_entry - import a label, return the list entry
* @string: a text string that might contain a Smack label at the beginning
* @len: the maximum size to look into, may be zero if string is null-terminated
*
* Returns a pointer to the entry in the label list that
* matches the passed string, adding it if necessary,
* or an error code.
*/
struct smack_known *smk_import_entry(const char *string, int len)
{
char *smack = smk_parse_smack(string, len);
if (IS_ERR(smack))
return ERR_CAST(smack);
return smk_import_allocated_label(smack, GFP_NOFS);
}
/**
* smk_import_valid_label - import a label, return the list entry
* @label a text string that is a valid Smack label, not null-terminated
*
* Returns: see description of smk_import_entry()
*/
struct smack_known *
smk_import_valid_label(const char *label, int label_len, gfp_t gfp)
{
char *smack = kstrndup(label, label_len, gfp);
if (!smack)
return ERR_PTR(-ENOMEM);
return smk_import_allocated_label(smack, gfp);
}
/**
* smack_from_secid - find the Smack label associated with a secid
* @secid: an integer that might be associated with a Smack label

117
security/smack/smack_lsm.c
View File

@ -3710,7 +3710,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
* @attr: which attribute to fetch
* @ctx: buffer to receive the result
* @size: available size in, actual size out
* @flags: unused
* @flags: reserved, currently zero
*
* Fill the passed user space @ctx with the details of the requested
* attribute.
@ -3771,57 +3771,52 @@ static int smack_getprocattr(struct task_struct *p, const char *name, char **val
* Sets the Smack value of the task. Only setting self
* is permitted and only with privilege
*
* Returns the length of the smack label or an error code
* Returns zero on success or an error code
*/
static int do_setattr(u64 attr, void *value, size_t size)
static int do_setattr(unsigned int attr, void *value, size_t size)
{
struct task_smack *tsp = smack_cred(current_cred());
struct cred *new;
struct smack_known *skp;
char *labelstr;
int rc = 0;
if (!smack_privileged(CAP_MAC_ADMIN) && list_empty(&tsp->smk_relabel))
return -EPERM;
int label_len;
/*
* let unprivileged user validate input, check permissions later
*/
if (value == NULL || size == 0 || size >= SMK_LONGLABEL)
return -EINVAL;
if (attr != LSM_ATTR_CURRENT)
return -EOPNOTSUPP;
labelstr = smk_parse_smack(value, size);
if (IS_ERR(labelstr))
return PTR_ERR(labelstr);
label_len = smk_parse_label_len(value, size);
if (label_len < 0 || label_len != size)
return -EINVAL;
/*
* No process is ever allowed the web ("@") label
* and the star ("*") label.
*/
if (labelstr[1] == '\0' /* '@', '*' */) {
const char c = labelstr[0];
if (label_len == 1 /* '@', '*' */) {
const char c = *(const char *)value;
if (c == *smack_known_web.smk_known ||
c == *smack_known_star.smk_known) {
rc = -EPERM;
goto free_labelstr;
}
c == *smack_known_star.smk_known)
return -EPERM;
}
if (!smack_privileged(CAP_MAC_ADMIN)) {
const struct smack_known_list_elem *sklep;
list_for_each_entry(sklep, &tsp->smk_relabel, list)
if (strcmp(sklep->smk_label->smk_known, labelstr) == 0)
goto free_labelstr;
rc = -EPERM;
list_for_each_entry(sklep, &tsp->smk_relabel, list) {
const char *cp = sklep->smk_label->smk_known;
if (strlen(cp) == label_len &&
strncmp(cp, value, label_len) == 0)
goto in_relabel;
}
return -EPERM;
in_relabel:
;
}
free_labelstr:
kfree(labelstr);
if (rc)
return -EPERM;
skp = smk_import_entry(value, size);
skp = smk_import_valid_label(value, label_len, GFP_KERNEL);
if (IS_ERR(skp))
return PTR_ERR(skp);
@ -3837,7 +3832,7 @@ free_labelstr:
smk_destroy_label_list(&tsp->smk_relabel);
commit_creds(new);
return size;
return 0;
}
/**
@ -3845,7 +3840,7 @@ free_labelstr:
* @attr: which attribute to set
* @ctx: buffer containing the data
* @size: size of @ctx
* @flags: unused
* @flags: reserved, must be zero
*
* Fill the passed user space @ctx with the details of the requested
* attribute.
@ -3855,12 +3850,26 @@ free_labelstr:
static int smack_setselfattr(unsigned int attr, struct lsm_ctx *ctx,
u32 size, u32 flags)
{
int rc;
if (attr != LSM_ATTR_CURRENT)
return -EOPNOTSUPP;
rc = do_setattr(attr, ctx->ctx, ctx->ctx_len);
if (rc > 0)
return 0;
return rc;
if (ctx->flags)
return -EINVAL;
/*
* string must have \0 terminator, included in ctx->ctx
* (see description of struct lsm_ctx)
*/
if (ctx->ctx_len == 0)
return -EINVAL;
if (ctx->ctx[ctx->ctx_len - 1] != '\0')
return -EINVAL;
/*
* other do_setattr() caller, smack_setprocattr(),
* does not count \0 into size, so
* decreasing length by 1 to accommodate the divergence.
*/
return do_setattr(attr, ctx->ctx, ctx->ctx_len - 1);
}
/**
@ -3872,15 +3881,39 @@ static int smack_setselfattr(unsigned int attr, struct lsm_ctx *ctx,
* Sets the Smack value of the task. Only setting self
* is permitted and only with privilege
*
* Returns the length of the smack label or an error code
* Returns the size of the input value or an error code
*/
static int smack_setprocattr(const char *name, void *value, size_t size)
{
int attr = lsm_name_to_attr(name);
size_t realsize = size;
unsigned int attr = lsm_name_to_attr(name);
if (attr != LSM_ATTR_UNDEF)
return do_setattr(attr, value, size);
return -EINVAL;
switch (attr) {
case LSM_ATTR_UNDEF: return -EINVAL;
default: return -EOPNOTSUPP;
case LSM_ATTR_CURRENT:
;
}
/*
* The value for the "current" attribute is the label
* followed by one of the 4 trailers: none, \0, \n, \n\0
*
* I.e. following inputs are accepted as 3-characters long label "foo":
*
* "foo" (3 characters)
* "foo\0" (4 characters)
* "foo\n" (4 characters)
* "foo\n\0" (5 characters)
*/
if (realsize && (((const char *)value)[realsize - 1] == '\0'))
--realsize;
if (realsize && (((const char *)value)[realsize - 1] == '\n'))
--realsize;
return do_setattr(attr, value, realsize) ? : size;
}
/**