Re: [PATCH] scripts/common: fix write_file when opened with mmap

[Andrej Picej <andrej.picej@norik.com>]

Hi Sascha,

On 31. 01. 22 10:23, Sascha Hauer wrote:
> Hi Andrej,
> 
> On Fri, Jan 28, 2022 at 09:00:33AM +0100, Andrej Picej wrote:
>> Usage of bareboximd with -c option (Create checksum for FILE and write
>> it to the crc32 tag) was broken. Possibly by applying 2154de1cf36c
>> (bareboximd: Use mmap when possibly). The script fails with:
>>
>>      $ ./scripts/bareboximd -c images/<barebox-image.img>
>>      Cannot write to images/<barebox-mage.img>: Bad address
>>      CRC: write crc token to images/<barebox-image.img> failed: -14
>>      Bad address
>>
>> This has to do with the usage of "mmap" and "open" with O_TRUNC flag
>> which truncates the file length to 0. Writing to files fails with:
>> EFAULT (14) buf is outside your accessible address space.
>> Remove the truncate flag and truncate manually after writing the data.
>>
>> This fixes the bareboximd script, which is now again usable with -c
>> option.
> 
> That's a very unfortunate bug :(
> 
>>
>> Signed-off-by: Anze Lesnik <anze.lesnik@norik.com>
>> Signed-off-by: Andrej Picej <andrej.picej@norik.com>
>> ---
>>   scripts/common.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/scripts/common.c b/scripts/common.c
>> index 3f8dcd2d38..331988d593 100644
>> --- a/scripts/common.c
>> +++ b/scripts/common.c
>> @@ -107,7 +107,7 @@ int write_file(const char *filename, const void *buf, size_t size)
>>   	int fd, ret = 0;
>>   	int now;
>>   
>> -	fd = open(filename, O_WRONLY | O_TRUNC | O_CREAT,
> 
> I added a comment above this while applying to prevent people from
> "optimizing" this patch away.
> 
>> +	fd = open(filename, O_WRONLY | O_CREAT,
>>   		  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
>>   	if (fd < 0) {
>>   		fprintf(stderr, "Cannot open %s: %s\n", filename, strerror(errno));
>> @@ -126,6 +126,11 @@ int write_file(const char *filename, const void *buf, size_t size)
>>   		buf += now;
>>   	}
>>   
>> +	if (ftruncate(fd, now) < 0) {
>> +		fprintf(stderr, "Cannot truncate file: %s", strerror(errno));
>> +		ret = -errno;
>> +	}
> 
> truncating to 'now' is only correct when we were able to write all bytes
> at once. Otherwise we must truncate to the input size. I fixed this up
> to the patch below.

That makes sense. Good thing you caught that.

Thanks.

> 
> Sascha
> 
> -----------------------------8<----------------------------
> 
>  From 738601e1258c55953284ee10801b26b9977918c2 Mon Sep 17 00:00:00 2001
> From: Andrej Picej <andrej.picej@norik.com>
> Date: Fri, 28 Jan 2022 09:00:33 +0100
> Subject: [PATCH] scripts/common: fix write_file when opened with mmap
> 
> Usage of bareboximd with -c option (Create checksum for FILE and write
> it to the crc32 tag) was broken. Possibly by applying 2154de1cf36c
> (bareboximd: Use mmap when possibly). The script fails with:
> 
>      $ ./scripts/bareboximd -c images/<barebox-image.img>
>      Cannot write to images/<barebox-mage.img>: Bad address
>      CRC: write crc token to images/<barebox-image.img> failed: -14
>      Bad address
> 
> This has to do with the usage of "mmap" and "open" with O_TRUNC flag
> which truncates the file length to 0. Writing to files fails with:
> EFAULT (14) buf is outside your accessible address space.
> Remove the truncate flag and truncate manually after writing the data.
> 
> This fixes the bareboximd script, which is now again usable with -c
> option.
> 
> Signed-off-by: Anze Lesnik <anze.lesnik@norik.com>
> Signed-off-by: Andrej Picej <andrej.picej@norik.com>
> Link: https://lore.barebox.org/20220128080033.167251-1-andrej.picej@norik.com
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>   scripts/common.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/scripts/common.c b/scripts/common.c
> index b780b09941..154d6dffcb 100644
> --- a/scripts/common.c
> +++ b/scripts/common.c
> @@ -105,26 +105,33 @@ int write_file(const char *filename, const void *buf, size_t size)
>   {
>   	int fd, ret = 0;
>   	int now;
> +	size_t left = size;
>   
> -	fd = open(filename, O_WRONLY | O_TRUNC | O_CREAT,
> +	/* The same file may be mmapped currently, so can't use O_TRUNC here */
> +	fd = open(filename, O_WRONLY | O_CREAT,
>   		  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
>   	if (fd < 0) {
>   		fprintf(stderr, "Cannot open %s: %s\n", filename, strerror(errno));
>   		return -errno;
>   	}
>   
> -	while (size) {
> -		now = write(fd, buf, size);
> +	while (left) {
> +		now = write(fd, buf, left);
>   		if (now < 0) {
>   			fprintf(stderr, "Cannot write to %s: %s\n", filename,
>   				strerror(errno));
>   			ret = -errno;
>   			goto out;
>   		}
> -		size -= now;
> +		left -= now;
>   		buf += now;
>   	}
>   
> +	if (ftruncate(fd, size) < 0) {
> +		fprintf(stderr, "Cannot truncate file: %s", strerror(errno));
> +		ret = -errno;
> +	}
> +
>   out:
>   	close(fd);
>   
> 

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