[PATCH AUTOSEL 4.4 7/7] altera-stapl: altera_get_note: prevent write beyond end of 'key'

[Sasha Levin <sashal@kernel.org>]

From: Daniel Axtens <dja@axtens.net>

[ Upstream commit 3745488e9d599916a0b40d45d3f30e3d4720288e ]

altera_get_note is called from altera_init, where key is kzalloc(33).

When the allocation functions are annotated to allow the compiler to see
the sizes of objects, and with FORTIFY_SOURCE, we see:

In file included from drivers/misc/altera-stapl/altera.c:14:0:
In function ‘strlcpy’,
    inlined from ‘altera_init’ at drivers/misc/altera-stapl/altera.c:2189:5:
include/linux/string.h:378:4: error: call to ‘__write_overflow’ declared with attribute error: detected write beyond size of object passed as 1st parameter
    __write_overflow();
    ^~~~~~~~~~~~~~~~~~

That refers to this code in altera_get_note:

    if (key != NULL)
            strlcpy(key, &p[note_strings +
                            get_unaligned_be32(
                            &p[note_table + (8 * i)])],
                    length);

The error triggers because the length of 'key' is 33, but the copy
uses length supplied as the 'length' parameter, which is always
256. Split the size parameter into key_len and val_len, and use the
appropriate length depending on what is being copied.

Detected by compiler error, only compile-tested.

Cc: "Igor M. Liplianin" <liplianin@netup.ru>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Link: https://lore.kernel.org/r/20200120074344.504-2-dja@axtens.net
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/202002251042.D898E67AC@keescook
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/misc/altera-stapl/altera.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/misc/altera-stapl/altera.c b/drivers/misc/altera-stapl/altera.c
index 494e263daa748..b7ee8043a133e 100644
--- a/drivers/misc/altera-stapl/altera.c
+++ b/drivers/misc/altera-stapl/altera.c
@@ -2126,8 +2126,8 @@ static int altera_execute(struct altera_state *astate,
 	return status;
 }
 
-static int altera_get_note(u8 *p, s32 program_size,
-			s32 *offset, char *key, char *value, int length)
+static int altera_get_note(u8 *p, s32 program_size, s32 *offset,
+			   char *key, char *value, int keylen, int vallen)
 /*
  * Gets key and value of NOTE fields in the JBC file.
  * Can be called in two modes:  if offset pointer is NULL,
@@ -2184,7 +2184,7 @@ static int altera_get_note(u8 *p, s32 program_size,
 						&p[note_table + (8 * i) + 4])];
 
 				if (value != NULL)
-					strlcpy(value, value_ptr, length);
+					strlcpy(value, value_ptr, vallen);
 
 			}
 		}
@@ -2203,13 +2203,13 @@ static int altera_get_note(u8 *p, s32 program_size,
 				strlcpy(key, &p[note_strings +
 						get_unaligned_be32(
 						&p[note_table + (8 * i)])],
-					length);
+					keylen);
 
 			if (value != NULL)
 				strlcpy(value, &p[note_strings +
 						get_unaligned_be32(
 						&p[note_table + (8 * i) + 4])],
-					length);
+					vallen);
 
 			*offset = i + 1;
 		}
@@ -2463,7 +2463,7 @@ int altera_init(struct altera_config *config, const struct firmware *fw)
 			__func__, (format_version == 2) ? "Jam STAPL" :
 						"pre-standardized Jam 1.1");
 		while (altera_get_note((u8 *)fw->data, fw->size,
-					&offset, key, value, 256) == 0)
+					&offset, key, value, 32, 256) == 0)
 			printk(KERN_INFO "%s: NOTE \"%s\" = \"%s\"\n",
 					__func__, key, value);
 	}
-- 
2.20.1