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Message-ID: <1423571552.31903.468.camel@linux.intel.com>
Date: Tue, 10 Feb 2015 14:32:32 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Trond Myklebust <trond.myklebust@...marydata.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
"David S. Miller" <davem@...emloft.net>,
linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH v3 3/3] lib/string_helpers.c: Change semantics of
string_escape_mem
On Tue, 2015-02-10 at 00:44 +0100, Rasmus Villemoes wrote:
> The current semantics of string_escape_mem are inadequate for one of
> its current users, vsnprintf(). If that is to honour its contract, it
> must know how much space would be needed for the entire escaped
> buffer, and string_escape_mem provides no way of obtaining that (short
> of allocating a large enough buffer (~4 times input string) to let it
> play with, and that's definitely a big no-no inside vsnprintf).
>
> So change the semantics for string_escape_mem to be more
> snprintf-like: Return the size of the output that would be generated
> if the destination buffer was big enough, but of course still only
> write to the part of dst it is allowed to, and don't do
> '\0'-termination. It is then up to the caller to detect whether output
> was truncated and to append a '\0' if desired. Also, we must output
> partial escape sequences, otherwise a call such as snprintf(buf, 3,
> "%1pE", "\123") would cause printf to write a \0 to buf[2] but leaving
> buf[0] and buf[1] with whatever they previously contained.
>
> This also fixes a bug in the escaped_string() helper function, which
> used to unconditionally pass a length of "end-buf" to
> string_escape_mem(); since the latter doesn't check osz for being
> insanely large, it would happily write to dst. For example,
> kasprintf(GFP_KERNEL, "something and then %pE", ...); is an easy way
> to trigger an oops.
>
> In test-string_helpers.c, I removed the now meaningless -ENOMEM test,
> and replaced it with testing for getting the expected return value
> even if the buffer is too small. Also ensure that nothing is written
> when osz == 0.
>
> In net/sunrpc/cache.c, I think qword_add still has the same
> semantics. Someone should definitely double-check this.
Thanks for an update. My comments below.
After addressing 'em, wrt changes to patch 2/3, take my
Acked-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
for all parts except net/sunrpc/cache.c.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
> include/linux/string_helpers.h | 8 ++++----
> lib/string_helpers.c | 39 +++++++--------------------------------
> lib/test-string_helpers.c | 35 +++++++++++++++--------------------
> lib/vsprintf.c | 8 ++++++--
> net/sunrpc/cache.c | 8 +++++---
> 5 files changed, 37 insertions(+), 61 deletions(-)
>
> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
> index 6eb567ac56bc..38a2a6f1fc76 100644
> --- a/include/linux/string_helpers.h
> +++ b/include/linux/string_helpers.h
> @@ -47,22 +47,22 @@ static inline int string_unescape_any_inplace(char *buf)
> #define ESCAPE_ANY_NP (ESCAPE_ANY | ESCAPE_NP)
> #define ESCAPE_HEX 0x20
>
> -int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
> +int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
> unsigned int flags, const char *esc);
>
> static inline int string_escape_mem_any_np(const char *src, size_t isz,
> - char **dst, size_t osz, const char *esc)
> + char *dst, size_t osz, const char *esc)
> {
> return string_escape_mem(src, isz, dst, osz, ESCAPE_ANY_NP, esc);
> }
>
> -static inline int string_escape_str(const char *src, char **dst, size_t sz,
> +static inline int string_escape_str(const char *src, char *dst, size_t sz,
> unsigned int flags, const char *esc)
> {
> return string_escape_mem(src, strlen(src), dst, sz, flags, esc);
> }
>
> -static inline int string_escape_str_any_np(const char *src, char **dst,
> +static inline int string_escape_str_any_np(const char *src, char *dst,
> size_t sz, const char *esc)
> {
> return string_escape_str(src, dst, sz, ESCAPE_ANY_NP, esc);
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index 7e2fef1eb40e..df7fda90b333 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -278,14 +278,11 @@ static bool escape_space(unsigned char c, char **dst, char *end)
> return false;
> }
>
> - if (out + 1 >= end)
> - goto skip;
> if (out + 0 < end)
> out[0] = '\\';
> if (out + 1 < end)
> out[1] = to;
>
> -skip:
> *dst = out + 2;
> return true;
> }
> @@ -309,14 +306,11 @@ static bool escape_special(unsigned char c, char **dst, char *end)
> return false;
> }
>
> - if (out + 1 >= end)
> - goto skip;
> if (out + 0 < end)
> out[0] = '\\';
> if (out + 1 < end)
> out[1] = to;
>
> -skip:
> *dst = out + 2;
> return true;
> }
> @@ -328,14 +322,11 @@ static bool escape_null(unsigned char c, char **dst, char *end)
> if (c)
> return false;
>
> - if (out + 1 >= end)
> - goto skip;
> if (out + 0 < end)
> out[0] = '\\';
> if (out + 1 < end)
> out[1] = '0';
>
> -skip:
> *dst = out + 2;
> return true;
> }
> @@ -344,8 +335,6 @@ static bool escape_octal(unsigned char c, char **dst, char *end)
> {
> char *out = *dst;
>
> - if (out + 3 >= end)
> - goto skip;
> if (out + 0 < end)
> out[0] = '\\';
> if (out + 1 < end)
> @@ -355,7 +344,6 @@ static bool escape_octal(unsigned char c, char **dst, char *end)
> if (out + 3 < end)
> out[3] = ((c >> 0) & 0x07) + '0';
>
> -skip:
> *dst = out + 4;
> return true;
> }
> @@ -364,8 +352,6 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
> {
> char *out = *dst;
>
> - if (out + 3 >= end)
> - goto skip;
> if (out + 0 < end)
> out[0] = '\\';
> if (out + 1 < end)
> @@ -375,7 +361,6 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
> if (out + 3 < end)
> out[3] = hex_asc_lo(c);
>
> -skip:
> *dst = out + 4;
> return true;
> }
> @@ -429,20 +414,17 @@ skip:
> * it if needs.
> *
> * Return:
> - * The amount of the characters processed to the destination buffer, or
> - * %-ENOMEM if the size of buffer is not enough to put an escaped character is
> - * returned.
> - *
> - * Even in the case of error @dst pointer will be updated to point to the byte
> - * after the last processed character.
> + * The total size of the escaped output that would be generated for
> + * the given input and flags. To check whether the output was
> + * truncated, compare the return value to osz. There is room left in
> + * dst for a '\0' terminator if and only if ret < osz.
> */
> -int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
> +int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
> unsigned int flags, const char *esc)
> {
> - char *p = *dst;
> + char *p = dst;
> char *end = p + osz;
> bool is_dict = esc && *esc;
> - int ret;
>
> while (isz--) {
> unsigned char c = *src++;
> @@ -482,13 +464,6 @@ int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
> escape_passthrough(c, &p, end);
> }
>
> - if (p > end) {
> - *dst = end;
> - return -ENOMEM;
> - }
> -
> - ret = p - *dst;
> - *dst = p;
> - return ret;
> + return p - dst;
> }
> EXPORT_SYMBOL(string_escape_mem);
> diff --git a/lib/test-string_helpers.c b/lib/test-string_helpers.c
> index ab0d30e1e18f..5f759c3c2f60 100644
> --- a/lib/test-string_helpers.c
> +++ b/lib/test-string_helpers.c
> @@ -264,12 +264,12 @@ static __init void test_string_escape(const char *name,
> const struct test_string_2 *s2,
> unsigned int flags, const char *esc)
> {
> - int q_real = 512;
> - char *out_test = kmalloc(q_real, GFP_KERNEL);
> - char *out_real = kmalloc(q_real, GFP_KERNEL);
> + size_t out_size = 512;
> + char *out_test = kmalloc(out_size, GFP_KERNEL);
> + char *out_real = kmalloc(out_size, GFP_KERNEL);
> char *in = kmalloc(256, GFP_KERNEL);
> - char *buf = out_real;
> int p = 0, q_test = 0;
> + int q_real;
>
> if (!out_test || !out_real || !in)
> goto out;
> @@ -301,29 +301,26 @@ static __init void test_string_escape(const char *name,
> q_test += len;
> }
>
> - q_real = string_escape_mem(in, p, &buf, q_real, flags, esc);
> + q_real = string_escape_mem(in, p, out_real, out_size, flags, esc);
>
> test_string_check_buf(name, flags, in, p, out_real, q_real, out_test,
> q_test);
> +
> + memset(out_real, 'Z', out_size);
> + q_real = string_escape_mem(in, p, out_real, 0, flags, esc);
> + if (q_real != q_test)
> + pr_warn("Test '%s' failed: flags = %u, osz = 0, expected %d, got %d\n",
> + name, flags, q_test, q_real);
> + if (memchr_inv(out_real, 'Z', out_size))
> + pr_warn("Test '%s' failed: osz = 0 but string_escape_mem wrote to the buffer\n",
> + name);
> +
So, why couldn't we split this to separate test case? It seems I already
pointed this out.
> out:
> kfree(in);
> kfree(out_real);
> kfree(out_test);
> }
>
> -static __init void test_string_escape_nomem(void)
> -{
> - char *in = "\eb \\C\007\"\x90\r]";
> - char out[64], *buf = out;
> - int rc = -ENOMEM, ret;
> -
> - ret = string_escape_str_any_np(in, &buf, strlen(in), NULL);
> - if (ret == rc)
> - return;
> -
> - pr_err("Test 'escape nomem' failed: got %d instead of %d\n", ret, rc);
> -}
> -
> static int __init test_string_helpers_init(void)
> {
> unsigned int i;
> @@ -342,8 +339,6 @@ static int __init test_string_helpers_init(void)
> for (i = 0; i < (ESCAPE_ANY_NP | ESCAPE_HEX) + 1; i++)
> test_string_escape("escape 1", escape1, i, TEST_STRING_2_DICT_1);
>
> - test_string_escape_nomem();
> -
> return -EINVAL;
> }
> module_init(test_string_helpers_init);
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3568e3906777..58e1193eaa4b 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1159,8 +1159,12 @@ char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>
> len = spec.field_width < 0 ? 1 : spec.field_width;
>
> - /* Ignore the error. We print as many characters as we can */
> - string_escape_mem(addr, len, &buf, end - buf, flags, NULL);
> + /*
> + * string_escape_mem writes as many characters as it can to
'string_escape_mem() writes…'
> + * the given buffer, and returns the total size of the output
> + * had the buffer been big enough.
> + */
> + buf += string_escape_mem(addr, len, buf, buf < end ? end - buf : 0, flags, NULL);
>
> return buf;
> }
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index 33fb105d4352..22c4418057f4 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -1068,12 +1068,14 @@ void qword_add(char **bpp, int *lp, char *str)
> {
> char *bp = *bpp;
> int len = *lp;
> - int ret;
> + int ret, written;
>
> if (len < 0) return;
>
> - ret = string_escape_str(str, &bp, len, ESCAPE_OCTAL, "\\ \n\t");
> - if (ret < 0 || ret == len)
> + ret = string_escape_str(str, bp, len, ESCAPE_OCTAL, "\\ \n\t");
> + written = min(ret, len);
> + bp += written;
> + if (ret >= len)
> len = -1;
> else {
> len -= ret;
--
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy
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