6.18-stable review patch. If anyone has any objections, please let me know.
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From: Armin Wolf W_Armin@gmx.de
[ Upstream commit 25524b6190295577e4918c689644451365e6466d ]
Currently the function responsible for converting between utf16 and utf8 strings will ignore any characters that cannot be converted. This however also includes multi-byte characters that do not fit into the provided string buffer.
This can cause problems if such a multi-byte character is followed by a single-byte character. In such a case the multi-byte character might be ignored when the provided string buffer is too small, but the single-byte character might fit and is thus still copied into the resulting string.
Fix this by stop filling the provided string buffer once a character does not fit. In order to be able to do this extend utf32_to_utf8() to return useful errno codes instead of -1.
Fixes: 74675a58507e ("NLS: update handling of Unicode") Signed-off-by: Armin Wolf W_Armin@gmx.de Link: https://patch.msgid.link/20251111131125.3379-2-W_Armin@gmx.de Reviewed-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/nls/nls_base.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/fs/nls/nls_base.c b/fs/nls/nls_base.c index 18d597e49a194..d434c4463a8f7 100644 --- a/fs/nls/nls_base.c +++ b/fs/nls/nls_base.c @@ -94,7 +94,7 @@ int utf32_to_utf8(unicode_t u, u8 *s, int maxout)
l = u; if (l > UNICODE_MAX || (l & SURROGATE_MASK) == SURROGATE_PAIR) - return -1; + return -EILSEQ;
nc = 0; for (t = utf8_table; t->cmask && maxout; t++, maxout--) { @@ -110,7 +110,7 @@ int utf32_to_utf8(unicode_t u, u8 *s, int maxout) return nc; } } - return -1; + return -EOVERFLOW; } EXPORT_SYMBOL(utf32_to_utf8);
@@ -217,8 +217,16 @@ int utf16s_to_utf8s(const wchar_t *pwcs, int inlen, enum utf16_endian endian, inlen--; } size = utf32_to_utf8(u, op, maxout); - if (size == -1) { - /* Ignore character and move on */ + if (size < 0) { + if (size == -EILSEQ) { + /* Ignore character and move on */ + continue; + } + /* + * Stop filling the buffer with data once a character + * does not fit anymore. + */ + break; } else { op += size; maxout -= size;