[PATCH master] blspec: fix use-after-free of firmware search path

[Ahmad Fatoum]

firmware_set_searchpath() is used to temporarily extend firmware search
path when parsing boot spec files. It does so by first freeing the
original firmware pointer and then storing a pointer to a copy of the
new search path.

firmware_get_searchpath() returns this pointer without copying meaning
that following sequence causes a use-after-free:

        old_fws = firmware_get_searchpath();
        firmware_set_searchpath(fws); /* calls free(old_fws) */
        firmware_set_searchpath(old_fws);

Fix this by keeping around a copy of the search path.

Fixes: dfebbb0a5944 ("blspec: Set firmware searchpath")
Signed-off-by: Ahmad Fatoum <ah...@a3f.at>
---
 common/blspec.c    | 4 ++--
 common/firmware.c  | 4 ++--
 include/firmware.h | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/common/blspec.c b/common/blspec.c
index 6cb1fea9e876..158fd1e9a28c 100644
--- a/common/blspec.c
+++ b/common/blspec.c
@@ -75,8 +75,7 @@ static int blspec_boot(struct bootentry *be, int verbose, int 
dryrun)
        const char *abspath, *devicetree, *options, *initrd, *linuximage;
        const char *overlays;
        const char *appendroot;
-       const char *old_fws;
-       char *fws;
+       char *old_fws, *fws;
        struct bootm_data data = {
                .dryrun = dryrun,
        };
@@ -158,6 +157,7 @@ static int blspec_boot(struct bootentry *be, int verbose, 
int dryrun)
 
        of_overlay_set_basedir("/");
        firmware_set_searchpath(old_fws);
+       free(old_fws);
 
 err_out:
        free((char *)data.oftree_file);
diff --git a/common/firmware.c b/common/firmware.c
index b33acff77ff8..b87d7da38fa7 100644
--- a/common/firmware.c
+++ b/common/firmware.c
@@ -224,9 +224,9 @@ out:
 
 static char *firmware_path;
 
-const char *firmware_get_searchpath(void)
+char *firmware_get_searchpath(void)
 {
-       return firmware_path;
+       return strdup(firmware_path);
 }
 
 void firmware_set_searchpath(const char *path)
diff --git a/include/firmware.h b/include/firmware.h
index 0ffea5284086..2583342230ae 100644
--- a/include/firmware.h
+++ b/include/firmware.h
@@ -31,7 +31,7 @@ struct firmware_mgr *firmwaremgr_find(const char *);
 #ifdef CONFIG_FIRMWARE
 struct firmware_mgr *firmwaremgr_find_by_node(struct device_node *np);
 int firmwaremgr_load_file(struct firmware_mgr *, const char *path);
-const char *firmware_get_searchpath(void);
+char *firmware_get_searchpath(void);
 void firmware_set_searchpath(const char *path);
 #else
 static inline struct firmware_mgr *firmwaremgr_find_by_node(struct device_node 
*np)
@@ -44,7 +44,7 @@ static inline int firmwaremgr_load_file(struct firmware_mgr 
*mgr, const char *pa
        return -ENOSYS;
 }
 
-static inline const char *firmware_get_searchpath(void)
+static inline char *firmware_get_searchpath(void)
 {
        return NULL;
 }
-- 
2.33.0


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