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buflib: remove the 'name' member from union buflib_data

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Using a length 1 char array to point to the name buffer triggers
a -Warray-bounds warning from GCC when fortified strcpy is used.

This type of construct isn't safe in general -- if the compiler
makes assumptions based on the array bound it can create subtle
bugs when accessing the array out of bounds.

Instead, add a function get_block_name() which returns a pointer
to the name field by casting. This suppresses the warning and it
should be a bit more portable.

Change-Id: I25d4f46f799022ad0ec23bef0218f7595cc741ea
This commit is contained in:
Aidan MacDonald 2022-03-30 20:55:14 +01:00
parent 6e9b1b344b
commit 8f896b14d3
2 changed files with 9 additions and 5 deletions
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13
firmware/buflib.c
View file

@ -187,6 +187,11 @@ static void check_block_crc(struct buflib_context *ctx,
union buflib_data *block,
union buflib_data *block_end);
static inline char* get_block_name(union buflib_data *block)
{
return (char*)&block[fidx_NAME];
}
/* Initialize buffer manager */
void
buflib_init(struct buflib_context *ctx, void *buf, size_t size)
@ -378,7 +383,7 @@ move_block(struct buflib_context* ctx, union buflib_data* block, int shift)
int handle = ctx->handle_table - h_entry;
BDEBUGF("%s(): moving \"%s\"(id=%d) by %d(%d)\n", __func__,
block[fidx_NAME].name, handle, shift, shift*(int)sizeof(union buflib_data));
get_block_name(block), handle, shift, shift*(int)sizeof(union buflib_data));
new_block = block + shift;
new_start = h_entry->alloc + shift*sizeof(union buflib_data);
@ -726,7 +731,7 @@ buffer_alloc:
block[fidx_HANDLE].handle = handle;
block[fidx_OPS].ops = ops;
if (name_len > 0)
strcpy(block[fidx_NAME].name, name);
strcpy(get_block_name(block), name);
size_t bsize = BUFLIB_NUM_FIELDS + name_len/sizeof(union buflib_data);
union buflib_data *block_end = block + bsize;
@ -1037,7 +1042,7 @@ const char* buflib_get_name(struct buflib_context *ctx, int handle)
return NULL;
data -= len;
return data[fidx_NAME].name;
return get_block_name(data);
}
#ifdef DEBUG
@ -1095,7 +1100,7 @@ void buflib_print_block_at(struct buflib_context *ctx, int block_num,
{
snprintf(buf, bufsize, "%8p: val: %4ld (%s)",
block, (long)block->val,
block->val > 0 ? block[fidx_NAME].name : "<unallocated>");
block->val > 0 ? get_block_name(block) : "<unallocated>");
}
}
}

1
firmware/include/buflib.h
View file

@ -38,7 +38,6 @@ union buflib_data
intptr_t val; /* length of the block in n*sizeof(union buflib_data).
Includes buflib metadata overhead. A negative value
indicates block is unallocated */
char name[1]; /* name, actually a variable sized string */
struct buflib_callbacks* ops; /* callback functions for move and shrink. Can be NULL */
char* alloc; /* start of allocated memory area */
union buflib_data *handle; /* pointer to entry in the handle table.