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selinux: Fix selinux_sb_mnt_opts_compat()
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selinux_sb_mnt_opts_compat() is called under the sb_lock spinlock and
shouldn't be performing any memory allocations.  Fix this by parsing the
sids at the same time we're chopping up the security mount options
string and then using the pre-parsed sids when doing the comparison.

Fixes: cc274ae ("selinux: fix sleeping function called from invalid context")
Fixes: 69c4a42 ("lsm,selinux: add new hook to compare new mount to an existing mount")
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
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@scottmayhew @pcmoore
scottmayhew authored and pcmoore committed Feb 1, 2022
1 parent ecff305 commit b8b87fd
Showing 1 changed file with 41 additions and 34 deletions.
75 changes: 41 additions & 34 deletions security/selinux/hooks.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -341,6 +341,10 @@ static void inode_free_security(struct inode *inode)

struct selinux_mnt_opts {
const char *fscontext, *context, *rootcontext, *defcontext;
u32 fscontext_sid;
u32 context_sid;
u32 rootcontext_sid;
u32 defcontext_sid;
};

static void selinux_free_mnt_opts(void *mnt_opts)
Expand Down Expand Up @@ -597,15 +601,14 @@ static int bad_option(struct superblock_security_struct *sbsec, char flag,
return 0;
}

static int parse_sid(struct super_block *sb, const char *s, u32 *sid,
gfp_t gfp)
static int parse_sid(struct super_block *sb, const char *s, u32 *sid)
{
int rc = security_context_str_to_sid(&selinux_state, s,
sid, gfp);
sid, GFP_KERNEL);
if (rc)
pr_warn("SELinux: security_context_str_to_sid"
"(%s) failed for (dev %s, type %s) errno=%d\n",
s, sb->s_id, sb->s_type->name, rc);
s, sb ? sb->s_id : "?", sb ? sb->s_type->name : "?", rc);
return rc;
}

Expand Down Expand Up @@ -672,8 +675,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
*/
if (opts) {
if (opts->fscontext) {
rc = parse_sid(sb, opts->fscontext, &fscontext_sid,
GFP_KERNEL);
rc = parse_sid(sb, opts->fscontext, &fscontext_sid);
if (rc)
goto out;
if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid,
Expand All @@ -682,8 +684,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
sbsec->flags |= FSCONTEXT_MNT;
}
if (opts->context) {
rc = parse_sid(sb, opts->context, &context_sid,
GFP_KERNEL);
rc = parse_sid(sb, opts->context, &context_sid);
if (rc)
goto out;
if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid,
Expand All @@ -692,8 +693,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
sbsec->flags |= CONTEXT_MNT;
}
if (opts->rootcontext) {
rc = parse_sid(sb, opts->rootcontext, &rootcontext_sid,
GFP_KERNEL);
rc = parse_sid(sb, opts->rootcontext, &rootcontext_sid);
if (rc)
goto out;
if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid,
Expand All @@ -702,8 +702,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
sbsec->flags |= ROOTCONTEXT_MNT;
}
if (opts->defcontext) {
rc = parse_sid(sb, opts->defcontext, &defcontext_sid,
GFP_KERNEL);
rc = parse_sid(sb, opts->defcontext, &defcontext_sid);
if (rc)
goto out;
if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid,
Expand Down Expand Up @@ -995,21 +994,29 @@ static int selinux_add_opt(int token, const char *s, void **mnt_opts)
if (opts->context || opts->defcontext)
goto err;
opts->context = s;
if (selinux_initialized(&selinux_state))
parse_sid(NULL, s, &opts->context_sid);
break;
case Opt_fscontext:
if (opts->fscontext)
goto err;
opts->fscontext = s;
if (selinux_initialized(&selinux_state))
parse_sid(NULL, s, &opts->fscontext_sid);
break;
case Opt_rootcontext:
if (opts->rootcontext)
goto err;
opts->rootcontext = s;
if (selinux_initialized(&selinux_state))
parse_sid(NULL, s, &opts->rootcontext_sid);
break;
case Opt_defcontext:
if (opts->context || opts->defcontext)
goto err;
opts->defcontext = s;
if (selinux_initialized(&selinux_state))
parse_sid(NULL, s, &opts->defcontext_sid);
break;
}

Expand Down Expand Up @@ -2647,8 +2654,6 @@ static int selinux_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)
{
struct selinux_mnt_opts *opts = mnt_opts;
struct superblock_security_struct *sbsec = selinux_superblock(sb);
u32 sid;
int rc;

/*
* Superblock not initialized (i.e. no options) - reject if any
Expand All @@ -2665,34 +2670,36 @@ static int selinux_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)
return (sbsec->flags & SE_MNTMASK) ? 1 : 0;

if (opts->fscontext) {
rc = parse_sid(sb, opts->fscontext, &sid, GFP_NOWAIT);
if (rc)
if (opts->fscontext_sid == SECSID_NULL)
return 1;
if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid, sid))
else if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid,
opts->fscontext_sid))
return 1;
}
if (opts->context) {
rc = parse_sid(sb, opts->context, &sid, GFP_NOWAIT);
if (rc)
if (opts->context_sid == SECSID_NULL)
return 1;
if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid, sid))
else if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid,
opts->context_sid))
return 1;
}
if (opts->rootcontext) {
struct inode_security_struct *root_isec;

root_isec = backing_inode_security(sb->s_root);
rc = parse_sid(sb, opts->rootcontext, &sid, GFP_NOWAIT);
if (rc)
return 1;
if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid, sid))
if (opts->rootcontext_sid == SECSID_NULL)
return 1;
else {
struct inode_security_struct *root_isec;

root_isec = backing_inode_security(sb->s_root);
if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid,
opts->rootcontext_sid))
return 1;
}
}
if (opts->defcontext) {
rc = parse_sid(sb, opts->defcontext, &sid, GFP_NOWAIT);
if (rc)
if (opts->defcontext_sid == SECSID_NULL)
return 1;
if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid, sid))
else if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid,
opts->defcontext_sid))
return 1;
}
return 0;
Expand All @@ -2712,14 +2719,14 @@ static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
return 0;

if (opts->fscontext) {
rc = parse_sid(sb, opts->fscontext, &sid, GFP_KERNEL);
rc = parse_sid(sb, opts->fscontext, &sid);
if (rc)
return rc;
if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid, sid))
goto out_bad_option;
}
if (opts->context) {
rc = parse_sid(sb, opts->context, &sid, GFP_KERNEL);
rc = parse_sid(sb, opts->context, &sid);
if (rc)
return rc;
if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid, sid))
Expand All @@ -2728,14 +2735,14 @@ static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
if (opts->rootcontext) {
struct inode_security_struct *root_isec;
root_isec = backing_inode_security(sb->s_root);
rc = parse_sid(sb, opts->rootcontext, &sid, GFP_KERNEL);
rc = parse_sid(sb, opts->rootcontext, &sid);
if (rc)
return rc;
if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid, sid))
goto out_bad_option;
}
if (opts->defcontext) {
rc = parse_sid(sb, opts->defcontext, &sid, GFP_KERNEL);
rc = parse_sid(sb, opts->defcontext, &sid);
if (rc)
return rc;
if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid, sid))
Expand Down

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