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diff --git a/Tests/test_sgi_crash.py b/Tests/test_sgi_crash.py
index 93fc1464a..3dbacb241 100644
--- a/Tests/test_sgi_crash.py
+++ b/Tests/test_sgi_crash.py
@@ -1,15 +1,31 @@
 #!/usr/bin/env python
 import pytest
+
 from PIL import Image
 
 
-def test_crashes():
-    with open("Tests/images/sgi_crash.bin", "rb") as f:
+@pytest.mark.parametrize(
+    "test_file",
+    [
+        "Tests/images/sgi_overrun_expandrowF04.bin",
+        "Tests/images/sgi_crash.bin",
+        "Tests/images/crash-6b7f2244da6d0ae297ee0754a424213444e92778.sgi",
+        "Tests/images/ossfuzz-5730089102868480.sgi",
+        "Tests/images/crash-754d9c7ec485ffb76a90eeaab191ef69a2a3a3cd.sgi",
+        "Tests/images/crash-465703f71a0f0094873a3e0e82c9f798161171b8.sgi",
+        "Tests/images/crash-64834657ee604b8797bf99eac6a194c124a9a8ba.sgi",
+        "Tests/images/crash-abcf1c97b8fe42a6c68f1fb0b978530c98d57ced.sgi",
+        "Tests/images/crash-b82e64d4f3f76d7465b6af535283029eda211259.sgi",
+        "Tests/images/crash-c1b2595b8b0b92cc5f38b6635e98e3a119ade807.sgi",
+        "Tests/images/crash-db8bfa78b19721225425530c5946217720d7df4e.sgi",
+    ],
+)
+def test_crashes(test_file):
+    with open(test_file, "rb") as f:
         im = Image.open(f)
-        with pytest.raises(IOError):
+        with pytest.raises(OSError):
             im.load()
 
-
 def test_overrun_crashes():
     with open("Tests/images/sgi_overrun_expandrowF04.bin", "rb") as f:
         im = Image.open(f)
diff --git a/src/libImaging/SgiRleDecode.c b/src/libImaging/SgiRleDecode.c
index 324353ce9..4eef44ba5 100644
--- a/src/libImaging/SgiRleDecode.c
+++ b/src/libImaging/SgiRleDecode.c
@@ -6,7 +6,7 @@
  *
  * history:
  * 2017-07-28 mb    fixed for images larger than 64KB
- * 2017-07-20 mb	created
+ * 2017-07-20 mb    created
  *
  * Copyright (c) Mickael Bonfill 2017.
  *
@@ -20,105 +20,182 @@
 #define RLE_COPY_FLAG 0x80
 #define RLE_MAX_RUN 0x7f
 
-static void read4B(UINT32* dest, UINT8* buf)
-{
+static void
+read4B(UINT32 *dest, UINT8 *buf) {
     *dest = (UINT32)((buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3]);
 }
 
-static int expandrow(UINT8* dest, UINT8* src, int n, int z, int xsize)
-{
+/*
+   SgiRleDecoding is done in a single channel row oriented set of RLE chunks.
+
+   * The file is arranged as
+     - SGI Header
+     - Rle Offset Table
+     - Rle Length Table
+     - Scanline Data
+
+   * Each RLE atom is c->bpc bytes wide (1 or 2)
+
+   * Each RLE Chunk is [specifier atom] [ 1 or n data atoms ]
+
+   * Copy Atoms are a byte with the high bit set, and the low 7 are
+     the number of bytes to copy from the source to the
+     destination. e.g.
+
+         CBBBBBBBB or 0CHLHLHLHLHLHL   (B=byte, H/L = Hi low bytes)
+
+   * Run atoms do not have the high bit set, and the low 7 bits are
+     the number of copies of the next atom to copy to the
+     destination. e.g.:
+
+         RB -> BBBBB or RHL -> HLHLHLHLHL
+
+   The upshot of this is, there is no way to determine the required
+   length of the input buffer from reloffset and rlelength without
+   going through the data at that scan line.
+
+   Furthermore, there's no requirement that individual scan lines
+   pointed to from the rleoffset table are in any sort of order or
+   used only once, or even disjoint. There's also no requirement that
+   all of the data in the scan line area of the image file be used
+
+ */
+static int
+expandrow(UINT8 *dest, UINT8 *src, int n, int z, int xsize, UINT8 *end_of_buffer) {
+    /*
+     * n here is the number of rlechunks
+     * z is the number of channels, for calculating the interleave
+     *   offset to go to RGBA style pixels
+     * xsize is the row width
+     * end_of_buffer is the address of the end of the input buffer
+     */
+
     UINT8 pixel, count;
     int x = 0;
 
-    for (;n > 0; n--)
-    {
+    for (; n > 0; n--) {
+        if (src > end_of_buffer) {
+            return -1;
+        }
         pixel = *src++;
-        if (n == 1 && pixel != 0)
+        if (n == 1 && pixel != 0) {
             return n;
+        }
         count = pixel & RLE_MAX_RUN;
-        if (!count)
+        if (!count) {
             return count;
+        }
         if (x + count > xsize) {
             return -1;
         }
         x += count;
         if (pixel & RLE_COPY_FLAG) {
-            while(count--) {
+            if (src + count > end_of_buffer) {
+                return -1;
+            }
+            while (count--) {
                 *dest = *src++;
                 dest += z;
             }
 
-        }
-        else {
+        } else {
+            if (src > end_of_buffer) {
+                return -1;
+            }
             pixel = *src++;
             while (count--) {
                 *dest = pixel;
                 dest += z;
             }
         }
-
     }
     return 0;
 }
 
-static int expandrow2(UINT8* dest, const UINT8* src, int n, int z, int xsize)
-{
+static int
+expandrow2(UINT8 *dest, const UINT8 *src, int n, int z, int xsize, UINT8 *end_of_buffer) {
     UINT8 pixel, count;
     int x = 0;
 
-
-    for (;n > 0; n--)
-    {
+    for (; n > 0; n--) {
+        if (src + 1 > end_of_buffer) {
+            return -1;
+        }
         pixel = src[1];
-        src+=2;
-        if (n == 1 && pixel != 0)
+        src += 2;
+        if (n == 1 && pixel != 0) {
             return n;
+        }
         count = pixel & RLE_MAX_RUN;
-        if (!count)
+        if (!count) {
             return count;
+        }
         if (x + count > xsize) {
             return -1;
         }
         x += count;
         if (pixel & RLE_COPY_FLAG) {
-            while(count--) {
+            if (src + 2 * count > end_of_buffer) {
+                return -1;
+            }
+            while (count--) {
                 memcpy(dest, src, 2);
                 src += 2;
                 dest += z * 2;
             }
-        }
-        else {
+        } else {
+            if (src + 2 > end_of_buffer) {
+                return -1;
+            }
             while (count--) {
                 memcpy(dest, src, 2);
                 dest += z * 2;
             }
-            src+=2;
+            src += 2;
         }
     }
     return 0;
 }
 
-
 int
-ImagingSgiRleDecode(Imaging im, ImagingCodecState state,
-		    UINT8* buf, Py_ssize_t bytes)
-{
+ImagingSgiRleDecode(Imaging im, ImagingCodecState state, UINT8 *buf, Py_ssize_t bytes) {
     UINT8 *ptr;
     SGISTATE *c;
     int err = 0;
     int status;
 
+    /* size check */
+    if (im->xsize > INT_MAX / im->bands || im->ysize > INT_MAX / im->bands) {
+        state->errcode = IMAGING_CODEC_MEMORY;
+        return -1;
+    }
+
     /* Get all data from File descriptor */
-    c = (SGISTATE*)state->context;
+    c = (SGISTATE *)state->context;
     _imaging_seek_pyFd(state->fd, 0L, SEEK_END);
     c->bufsize = _imaging_tell_pyFd(state->fd);
     c->bufsize -= SGI_HEADER_SIZE;
+
+    c->tablen = im->bands * im->ysize;
+    /* below, we populate the starttab and lentab into the bufsize,
+       each with 4 bytes per element of tablen
+       Check here before we allocate any memory
+    */
+    if (c->bufsize < 8 * c->tablen) {
+        state->errcode = IMAGING_CODEC_OVERRUN;
+        return -1;
+    }
+
     ptr = malloc(sizeof(UINT8) * c->bufsize);
     if (!ptr) {
-        return IMAGING_CODEC_MEMORY;
+        state->errcode = IMAGING_CODEC_MEMORY;
+        return -1;
     }
     _imaging_seek_pyFd(state->fd, SGI_HEADER_SIZE, SEEK_SET);
-    _imaging_read_pyFd(state->fd, (char*)ptr, c->bufsize);
+    if (_imaging_read_pyFd(state->fd, (char *)ptr, c->bufsize) != c->bufsize) {
+        state->errcode = IMAGING_CODEC_UNKNOWN;
+        return -1;
+    }
 
 
     /* decoder initialization */
@@ -130,80 +207,82 @@ ImagingSgiRleDecode(Imaging im, ImagingCodecState state,
         state->ystep = 1;
     }
 
-    if (im->xsize > INT_MAX / im->bands ||
-        im->ysize > INT_MAX / im->bands) {
-        err = IMAGING_CODEC_MEMORY;
-        goto sgi_finish_decode;
-    }
-
     /* Allocate memory for RLE tables and rows */
     free(state->buffer);
     state->buffer = NULL;
     /* malloc overflow check above */
     state->buffer = calloc(im->xsize * im->bands, sizeof(UINT8) * 2);
-    c->tablen = im->bands * im->ysize;
     c->starttab = calloc(c->tablen, sizeof(UINT32));
     c->lengthtab = calloc(c->tablen, sizeof(UINT32));
-    if (!state->buffer ||
-        !c->starttab ||
-        !c->lengthtab) {
+    if (!state->buffer || !c->starttab || !c->lengthtab) {
         err = IMAGING_CODEC_MEMORY;
         goto sgi_finish_decode;
     }
     /* populate offsets table */
-    for (c->tabindex = 0, c->bufindex = 0; c->tabindex < c->tablen; c->tabindex++, c->bufindex+=4)
+    for (c->tabindex = 0, c->bufindex = 0; c->tabindex < c->tablen;
+         c->tabindex++, c->bufindex += 4) {
         read4B(&c->starttab[c->tabindex], &ptr[c->bufindex]);
+    }
     /* populate lengths table */
-    for (c->tabindex = 0, c->bufindex = c->tablen * sizeof(UINT32); c->tabindex < c->tablen; c->tabindex++, c->bufindex+=4)
+    for (c->tabindex = 0, c->bufindex = c->tablen * sizeof(UINT32);
+         c->tabindex < c->tablen;
+         c->tabindex++, c->bufindex += 4) {
         read4B(&c->lengthtab[c->tabindex], &ptr[c->bufindex]);
-
-    state->count += c->tablen * sizeof(UINT32) * 2;
+    }
 
     /* read compressed rows */
-    for (c->rowno = 0; c->rowno < im->ysize; c->rowno++, state->y += state->ystep)
-    {
-        for (c->channo = 0; c->channo < im->bands; c->channo++)
-        {
+    for (c->rowno = 0; c->rowno < im->ysize; c->rowno++, state->y += state->ystep) {
+        for (c->channo = 0; c->channo < im->bands; c->channo++) {
             c->rleoffset = c->starttab[c->rowno + c->channo * im->ysize];
             c->rlelength = c->lengthtab[c->rowno + c->channo * im->ysize];
+
+            // Check for underflow of rleoffset-SGI_HEADER_SIZE
+            if (c->rleoffset < SGI_HEADER_SIZE) {
+                state->errcode = IMAGING_CODEC_OVERRUN;
+                goto sgi_finish_decode;
+            }
+
             c->rleoffset -= SGI_HEADER_SIZE;
 
-            if (c->rleoffset + c->rlelength > c->bufsize) {
-                state->errcode = IMAGING_CODEC_OVERRUN;
-                return -1;
-            }
-
             /* row decompression */
-            if (c->bpc ==1) {
-                status = expandrow(&state->buffer[c->channo], &ptr[c->rleoffset], c->rlelength, im->bands, im->xsize);
-            }
-            else {
-                status = expandrow2(&state->buffer[c->channo * 2], &ptr[c->rleoffset], c->rlelength, im->bands, im->xsize);
+            if (c->bpc == 1) {
+                status = expandrow(
+                    &state->buffer[c->channo],
+                    &ptr[c->rleoffset],
+                    c->rlelength,
+                    im->bands,
+                    im->xsize,
+                    &ptr[c->bufsize-1]);
+            } else {
+                status = expandrow2(
+                    &state->buffer[c->channo * 2],
+                    &ptr[c->rleoffset],
+                    c->rlelength,
+                    im->bands,
+                    im->xsize,
+                    &ptr[c->bufsize-1]);
             }
             if (status == -1) {
                 state->errcode = IMAGING_CODEC_OVERRUN;
-                return -1;
+                goto sgi_finish_decode;
             } else if (status == 1) {
                 goto sgi_finish_decode;
             }
 
-            state->count += c->rlelength;
         }
 
         /* store decompressed data in image */
-        state->shuffle((UINT8*)im->image[state->y], state->buffer, im->xsize);
-
+        state->shuffle((UINT8 *)im->image[state->y], state->buffer, im->xsize);
     }
 
-    c->bufsize++;
-
-sgi_finish_decode: ;
+sgi_finish_decode:;
 
     free(c->starttab);
     free(c->lengthtab);
     free(ptr);
-    if (err != 0){
-        return err;
+    if (err != 0) {
+        state->errcode = err;
+        return -1;
     }
-    return state->count - c->bufsize;
+    return 0;
 }