| Message ID | 20221103113021.3271-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] unicode: don't write -1 after NUL terminator | expand |
"Jason A. Donenfeld" <Jason@zx2c4.com> writes: > If the intention is to overwrite the first NUL with a -1, s[strlen(s)] > is the first NUL, not s[strlen(s)+1]. Hi Jason, This code is part of the verification of the trie that done at the end of utf8data generation. It is making sure the tree is not corrupted, by ensuring that utf8byte doesn't see something past the correct end of the string (the first NULL byte). Note it is not a bad memory access either, since we guarantee to have allocated enough space. So I think the code is correct as is. if you apply your patch and regenerate utf8data.h_shipped, utf8byte will reach that -1 and fail the verification. > Cc: Gabriel Krisman Bertazi <krisman@collabora.com> > Cc: stable@vger.kernel.org > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > fs/unicode/mkutf8data.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/unicode/mkutf8data.c b/fs/unicode/mkutf8data.c > index bc1a7c8b5c8d..61800e0d3226 100644 > --- a/fs/unicode/mkutf8data.c > +++ b/fs/unicode/mkutf8data.c > @@ -3194,7 +3194,7 @@ static int normalize_line(struct tree *tree) > /* Second test: length-limited string. */ > s = buf2; > /* Replace NUL with a value that will cause an error if seen. */ > - s[strlen(s) + 1] = -1; > + s[strlen(s)] = -1; > t = buf3; > if (utf8cursor(&u8c, tree, s)) > return -1;
Hi Gabriel, On Mon, Nov 07, 2022 at 09:45:25AM -0500, Gabriel Krisman Bertazi wrote: > "Jason A. Donenfeld" <Jason@zx2c4.com> writes: > > > If the intention is to overwrite the first NUL with a -1, s[strlen(s)] > > is the first NUL, not s[strlen(s)+1]. > > Hi Jason, > > This code is part of the verification of the trie that done at the end > of utf8data generation. It is making sure the tree is not corrupted, by > ensuring that utf8byte doesn't see something past the correct end of the > string (the first NULL byte). Note it is not a bad memory access > either, since we guarantee to have allocated enough space. > > So I think the code is correct as is. if you apply your patch and > regenerate utf8data.h_shipped, utf8byte will reach that -1 and fail the > verification. Ah, okay. "Replace NUL" would seem to be wrong/confusing comment text I suppose. Thanks for the explanation anyhow, and sorry for the noise. Jason > > > Cc: Gabriel Krisman Bertazi <krisman@collabora.com> > > Cc: stable@vger.kernel.org > > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > > --- > > fs/unicode/mkutf8data.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/unicode/mkutf8data.c b/fs/unicode/mkutf8data.c > > index bc1a7c8b5c8d..61800e0d3226 100644 > > --- a/fs/unicode/mkutf8data.c > > +++ b/fs/unicode/mkutf8data.c > > @@ -3194,7 +3194,7 @@ static int normalize_line(struct tree *tree) > > /* Second test: length-limited string. */ > > s = buf2; > > /* Replace NUL with a value that will cause an error if seen. */ > > - s[strlen(s) + 1] = -1; > > + s[strlen(s)] = -1; > > t = buf3; > > if (utf8cursor(&u8c, tree, s)) > > return -1; > > -- > Gabriel Krisman Bertazi
diff --git a/fs/unicode/mkutf8data.c b/fs/unicode/mkutf8data.c index bc1a7c8b5c8d..61800e0d3226 100644 --- a/fs/unicode/mkutf8data.c +++ b/fs/unicode/mkutf8data.c @@ -3194,7 +3194,7 @@ static int normalize_line(struct tree *tree) /* Second test: length-limited string. */ s = buf2; /* Replace NUL with a value that will cause an error if seen. */ - s[strlen(s) + 1] = -1; + s[strlen(s)] = -1; t = buf3; if (utf8cursor(&u8c, tree, s)) return -1;
If the intention is to overwrite the first NUL with a -1, s[strlen(s)] is the first NUL, not s[strlen(s)+1]. Cc: Gabriel Krisman Bertazi <krisman@collabora.com> Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- fs/unicode/mkutf8data.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)