[Xen-devel] [PATCH 6/9] Decompressors: check for write errors in unlzma.c

["Jan Beulich" <JBeulich@xxxxxxxx>]

From: Lasse Collin <lasse.collin@xxxxxxxxxxx>

The return value of wr->flush() is not checked in write_byte().  This
means that the decompressor won't stop even if the caller doesn't want
more data.  This can happen e.g.  with corrupt LZMA-compressed initramfs.
Returning the error quickly allows the user to see the error message
quicker.

There is a similar missing check for wr.flush() near the end of unlzma().

Signed-off-by: Lasse Collin <lasse.collin@xxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/unlzma.c
+++ b/xen/common/unlzma.c
@@ -307,32 +307,38 @@ static inline uint8_t INIT peek_old_byte
 
 }
 
-static inline void INIT write_byte(struct writer *wr, uint8_t byte)
+static inline int INIT write_byte(struct writer *wr, uint8_t byte)
 {
        wr->buffer[wr->buffer_pos++] = wr->previous_byte = byte;
        if (wr->flush && wr->buffer_pos == wr->header->dict_size) {
                wr->buffer_pos = 0;
                wr->global_pos += wr->header->dict_size;
-               wr->flush((char *)wr->buffer, wr->header->dict_size);
+               if (wr->flush((char *)wr->buffer, wr->header->dict_size)
+                               != wr->header->dict_size)
+                       return -1;
        }
+       return 0;
 }
 
 
-static inline void INIT copy_byte(struct writer *wr, uint32_t offs)
+static inline int INIT copy_byte(struct writer *wr, uint32_t offs)
 {
-       write_byte(wr, peek_old_byte(wr, offs));
+       return write_byte(wr, peek_old_byte(wr, offs));
 }
 
-static inline void INIT copy_bytes(struct writer *wr,
+static inline int INIT copy_bytes(struct writer *wr,
                                         uint32_t rep0, int len)
 {
        do {
-               copy_byte(wr, rep0);
+               if (copy_byte(wr, rep0))
+                       return -1;
                len--;
        } while (len != 0 && wr->buffer_pos < wr->header->dst_size);
+
+       return len;
 }
 
-static inline void INIT process_bit0(struct writer *wr, struct rc *rc,
+static inline int INIT process_bit0(struct writer *wr, struct rc *rc,
                                     struct cstate *cst, uint16_t *p,
                                     int pos_state, uint16_t *prob,
                                     int lc, uint32_t literal_pos_mask) {
@@ -366,16 +372,17 @@ static inline void INIT process_bit0(str
                uint16_t *prob_lit = prob + mi;
                rc_get_bit(rc, prob_lit, &mi);
        }
-       write_byte(wr, mi);
        if (cst->state < 4)
                cst->state = 0;
        else if (cst->state < 10)
                cst->state -= 3;
        else
                cst->state -= 6;
+
+       return write_byte(wr, mi);
 }
 
-static inline void INIT process_bit1(struct writer *wr, struct rc *rc,
+static inline int INIT process_bit1(struct writer *wr, struct rc *rc,
                                            struct cstate *cst, uint16_t *p,
                                            int pos_state, uint16_t *prob) {
   int offset;
@@ -406,8 +413,7 @@ static inline void INIT process_bit1(str
 
                                cst->state = cst->state < LZMA_NUM_LIT_STATES ?
                                        9 : 11;
-                               copy_byte(wr, cst->rep0);
-                               return;
+                               return copy_byte(wr, cst->rep0);
                        } else {
                                rc_update_bit_1(rc, prob);
                        }
@@ -509,12 +515,12 @@ static inline void INIT process_bit1(str
                } else
                        cst->rep0 = pos_slot;
                if (++(cst->rep0) == 0)
-                       return;
+                       return 0;
        }
 
        len += LZMA_MATCH_MIN_LEN;
 
-       copy_bytes(wr, cst->rep0, len);
+       return copy_bytes(wr, cst->rep0, len);
 }
 
 
@@ -617,11 +623,17 @@ STATIC int INIT unlzma(unsigned char *bu
                int pos_state = get_pos(&wr) & pos_state_mask;
                uint16_t *prob = p + LZMA_IS_MATCH +
                        (cst.state << LZMA_NUM_POS_BITS_MAX) + pos_state;
-               if (rc_is_bit_0(&rc, prob))
-                       process_bit0(&wr, &rc, &cst, p, pos_state, prob,
-                                    lc, literal_pos_mask);
-               else {
-                       process_bit1(&wr, &rc, &cst, p, pos_state, prob);
+               if (rc_is_bit_0(&rc, prob)) {
+                       if (process_bit0(&wr, &rc, &cst, p, pos_state, prob,
+                                       lc, literal_pos_mask)) {
+                               error("LZMA data is corrupt");
+                               goto exit_3;
+                       }
+               } else {
+                       if (process_bit1(&wr, &rc, &cst, p, pos_state, prob)) {
+                               error("LZMA data is corrupt");
+                               goto exit_3;
+                       }
                        if (cst.rep0 == 0)
                                break;
                }
@@ -631,9 +643,8 @@ STATIC int INIT unlzma(unsigned char *bu
 
        if (posp)
                *posp = rc.ptr-rc.buffer;
-       if (wr.flush)
-               wr.flush(wr.buffer, wr.buffer_pos);
-       ret = 0;
+       if (!wr.flush || wr.flush(wr.buffer, wr.buffer_pos) == wr.buffer_pos)
+               ret = 0;
 exit_3:
        large_free(p);
 exit_2:

Attachment: unlzma-check-write-errors.patch
Description: Text document

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